author | kleing |
Wed, 14 Apr 2004 14:13:05 +0200 | |
changeset 14565 | c6dc17aab88a |
parent 13515 | a6a7025fd7e8 |
child 14710 | 247615bfffb8 |
permissions | -rw-r--r-- |
wenzelm@7917 | 1 |
(* Title: HOL/Real/HahnBanach/VectorSpace.thy |
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ID: $Id$ |
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Author: Gertrud Bauer, TU Munich |
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*) |
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|
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header {* Vector spaces *} |
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|
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theory VectorSpace = Aux: |
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|
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subsection {* Signature *} |
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|
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text {* |
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For the definition of real vector spaces a type @{typ 'a} of the |
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sort @{text "{plus, minus, zero}"} is considered, on which a real |
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scalar multiplication @{text \<cdot>} is declared. |
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*} |
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|
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consts |
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prod :: "real \<Rightarrow> 'a::{plus, minus, zero} \<Rightarrow> 'a" (infixr "'(*')" 70) |
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|
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syntax (xsymbols) |
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prod :: "real \<Rightarrow> 'a \<Rightarrow> 'a" (infixr "\<cdot>" 70) |
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syntax (HTML output) |
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prod :: "real \<Rightarrow> 'a \<Rightarrow> 'a" (infixr "\<cdot>" 70) |
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|
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|
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subsection {* Vector space laws *} |
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|
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text {* |
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A \emph{vector space} is a non-empty set @{text V} of elements from |
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@{typ 'a} with the following vector space laws: The set @{text V} is |
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closed under addition and scalar multiplication, addition is |
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associative and commutative; @{text "- x"} is the inverse of @{text |
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x} w.~r.~t.~addition and @{text 0} is the neutral element of |
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addition. Addition and multiplication are distributive; scalar |
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multiplication is associative and the real number @{text "1"} is |
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the neutral element of scalar multiplication. |
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*} |
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|
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locale vectorspace = var V + |
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assumes non_empty [iff, intro?]: "V \<noteq> {}" |
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and add_closed [iff]: "x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> x + y \<in> V" |
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and mult_closed [iff]: "x \<in> V \<Longrightarrow> a \<cdot> x \<in> V" |
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and add_assoc: "x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> z \<in> V \<Longrightarrow> (x + y) + z = x + (y + z)" |
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and add_commute: "x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> x + y = y + x" |
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and diff_self [simp]: "x \<in> V \<Longrightarrow> x - x = 0" |
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and add_zero_left [simp]: "x \<in> V \<Longrightarrow> 0 + x = x" |
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and add_mult_distrib1: "x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> a \<cdot> (x + y) = a \<cdot> x + a \<cdot> y" |
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and add_mult_distrib2: "x \<in> V \<Longrightarrow> (a + b) \<cdot> x = a \<cdot> x + b \<cdot> x" |
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and mult_assoc: "x \<in> V \<Longrightarrow> (a * b) \<cdot> x = a \<cdot> (b \<cdot> x)" |
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and mult_1 [simp]: "x \<in> V \<Longrightarrow> 1 \<cdot> x = x" |
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and negate_eq1: "x \<in> V \<Longrightarrow> - x = (- 1) \<cdot> x" |
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and diff_eq1: "x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> x - y = x + - y" |
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|
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lemma (in vectorspace) negate_eq2: "x \<in> V \<Longrightarrow> (- 1) \<cdot> x = - x" |
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by (rule negate_eq1 [symmetric]) |
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|
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lemma (in vectorspace) negate_eq2a: "x \<in> V \<Longrightarrow> -1 \<cdot> x = - x" |
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by (simp add: negate_eq1) |
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|
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lemma (in vectorspace) diff_eq2: "x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> x + - y = x - y" |
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by (rule diff_eq1 [symmetric]) |
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|
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lemma (in vectorspace) diff_closed [iff]: "x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> x - y \<in> V" |
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by (simp add: diff_eq1 negate_eq1) |
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|
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lemma (in vectorspace) neg_closed [iff]: "x \<in> V \<Longrightarrow> - x \<in> V" |
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by (simp add: negate_eq1) |
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|
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lemma (in vectorspace) add_left_commute: |
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"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> z \<in> V \<Longrightarrow> x + (y + z) = y + (x + z)" |
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proof - |
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assume xyz: "x \<in> V" "y \<in> V" "z \<in> V" |
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hence "x + (y + z) = (x + y) + z" |
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by (simp only: add_assoc) |
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also from xyz have "... = (y + x) + z" by (simp only: add_commute) |
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also from xyz have "... = y + (x + z)" by (simp only: add_assoc) |
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finally show ?thesis . |
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qed |
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|
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theorems (in vectorspace) add_ac = |
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add_assoc add_commute add_left_commute |
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|
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|
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text {* The existence of the zero element of a vector space |
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follows from the non-emptiness of carrier set. *} |
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|
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lemma (in vectorspace) zero [iff]: "0 \<in> V" |
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proof - |
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from non_empty obtain x where x: "x \<in> V" by blast |
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then have "0 = x - x" by (rule diff_self [symmetric]) |
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also from x have "... \<in> V" by (rule diff_closed) |
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finally show ?thesis . |
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qed |
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|
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lemma (in vectorspace) add_zero_right [simp]: |
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"x \<in> V \<Longrightarrow> x + 0 = x" |
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proof - |
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assume x: "x \<in> V" |
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from this and zero have "x + 0 = 0 + x" by (rule add_commute) |
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also from x have "... = x" by (rule add_zero_left) |
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finally show ?thesis . |
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qed |
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|
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lemma (in vectorspace) mult_assoc2: |
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"x \<in> V \<Longrightarrow> a \<cdot> b \<cdot> x = (a * b) \<cdot> x" |
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by (simp only: mult_assoc) |
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|
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lemma (in vectorspace) diff_mult_distrib1: |
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"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> a \<cdot> (x - y) = a \<cdot> x - a \<cdot> y" |
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by (simp add: diff_eq1 negate_eq1 add_mult_distrib1 mult_assoc2) |
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|
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lemma (in vectorspace) diff_mult_distrib2: |
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"x \<in> V \<Longrightarrow> (a - b) \<cdot> x = a \<cdot> x - (b \<cdot> x)" |
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proof - |
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assume x: "x \<in> V" |
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have " (a - b) \<cdot> x = (a + - b) \<cdot> x" |
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by (simp add: real_diff_def) |
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also have "... = a \<cdot> x + (- b) \<cdot> x" |
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by (rule add_mult_distrib2) |
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also from x have "... = a \<cdot> x + - (b \<cdot> x)" |
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by (simp add: negate_eq1 mult_assoc2) |
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also from x have "... = a \<cdot> x - (b \<cdot> x)" |
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by (simp add: diff_eq1) |
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finally show ?thesis . |
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qed |
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|
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lemmas (in vectorspace) distrib = |
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add_mult_distrib1 add_mult_distrib2 |
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diff_mult_distrib1 diff_mult_distrib2 |
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|
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|
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text {* \medskip Further derived laws: *} |
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|
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lemma (in vectorspace) mult_zero_left [simp]: |
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"x \<in> V \<Longrightarrow> 0 \<cdot> x = 0" |
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proof - |
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assume x: "x \<in> V" |
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have "0 \<cdot> x = (1 - 1) \<cdot> x" by simp |
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also have "... = (1 + - 1) \<cdot> x" by simp |
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also have "... = 1 \<cdot> x + (- 1) \<cdot> x" |
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by (rule add_mult_distrib2) |
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also from x have "... = x + (- 1) \<cdot> x" by simp |
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also from x have "... = x + - x" by (simp add: negate_eq2a) |
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also from x have "... = x - x" by (simp add: diff_eq2) |
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also from x have "... = 0" by simp |
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finally show ?thesis . |
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qed |
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|
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lemma (in vectorspace) mult_zero_right [simp]: |
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"a \<cdot> 0 = (0::'a)" |
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proof - |
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have "a \<cdot> 0 = a \<cdot> (0 - (0::'a))" by simp |
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also have "... = a \<cdot> 0 - a \<cdot> 0" |
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by (rule diff_mult_distrib1) simp_all |
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also have "... = 0" by simp |
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finally show ?thesis . |
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qed |
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|
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lemma (in vectorspace) minus_mult_cancel [simp]: |
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"x \<in> V \<Longrightarrow> (- a) \<cdot> - x = a \<cdot> x" |
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by (simp add: negate_eq1 mult_assoc2) |
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|
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lemma (in vectorspace) add_minus_left_eq_diff: |
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"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> - x + y = y - x" |
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proof - |
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assume xy: "x \<in> V" "y \<in> V" |
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hence "- x + y = y + - x" by (simp add: add_commute) |
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also from xy have "... = y - x" by (simp add: diff_eq1) |
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finally show ?thesis . |
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qed |
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|
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lemma (in vectorspace) add_minus [simp]: |
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"x \<in> V \<Longrightarrow> x + - x = 0" |
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by (simp add: diff_eq2) |
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|
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lemma (in vectorspace) add_minus_left [simp]: |
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"x \<in> V \<Longrightarrow> - x + x = 0" |
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by (simp add: diff_eq2 add_commute) |
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|
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lemma (in vectorspace) minus_minus [simp]: |
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"x \<in> V \<Longrightarrow> - (- x) = x" |
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by (simp add: negate_eq1 mult_assoc2) |
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|
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lemma (in vectorspace) minus_zero [simp]: |
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"- (0::'a) = 0" |
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by (simp add: negate_eq1) |
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|
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lemma (in vectorspace) minus_zero_iff [simp]: |
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"x \<in> V \<Longrightarrow> (- x = 0) = (x = 0)" |
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proof |
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assume x: "x \<in> V" |
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{ |
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from x have "x = - (- x)" by (simp add: minus_minus) |
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also assume "- x = 0" |
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also have "- ... = 0" by (rule minus_zero) |
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finally show "x = 0" . |
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next |
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assume "x = 0" |
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then show "- x = 0" by simp |
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} |
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qed |
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|
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lemma (in vectorspace) add_minus_cancel [simp]: |
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"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> x + (- x + y) = y" |
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by (simp add: add_assoc [symmetric] del: add_commute) |
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|
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lemma (in vectorspace) minus_add_cancel [simp]: |
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"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> - x + (x + y) = y" |
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by (simp add: add_assoc [symmetric] del: add_commute) |
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|
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lemma (in vectorspace) minus_add_distrib [simp]: |
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"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> - (x + y) = - x + - y" |
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by (simp add: negate_eq1 add_mult_distrib1) |
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|
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lemma (in vectorspace) diff_zero [simp]: |
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"x \<in> V \<Longrightarrow> x - 0 = x" |
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by (simp add: diff_eq1) |
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|
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lemma (in vectorspace) diff_zero_right [simp]: |
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"x \<in> V \<Longrightarrow> 0 - x = - x" |
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by (simp add: diff_eq1) |
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|
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lemma (in vectorspace) add_left_cancel: |
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"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> z \<in> V \<Longrightarrow> (x + y = x + z) = (y = z)" |
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proof |
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assume x: "x \<in> V" and y: "y \<in> V" and z: "z \<in> V" |
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{ |
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from y have "y = 0 + y" by simp |
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also from x y have "... = (- x + x) + y" by simp |
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also from x y have "... = - x + (x + y)" |
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by (simp add: add_assoc neg_closed) |
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also assume "x + y = x + z" |
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also from x z have "- x + (x + z) = - x + x + z" |
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by (simp add: add_assoc [symmetric] neg_closed) |
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also from x z have "... = z" by simp |
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finally show "y = z" . |
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next |
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assume "y = z" |
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then show "x + y = x + z" by (simp only:) |
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} |
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qed |
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|
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lemma (in vectorspace) add_right_cancel: |
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"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> z \<in> V \<Longrightarrow> (y + x = z + x) = (y = z)" |
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by (simp only: add_commute add_left_cancel) |
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|
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lemma (in vectorspace) add_assoc_cong: |
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"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> x' \<in> V \<Longrightarrow> y' \<in> V \<Longrightarrow> z \<in> V |
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\<Longrightarrow> x + y = x' + y' \<Longrightarrow> x + (y + z) = x' + (y' + z)" |
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by (simp only: add_assoc [symmetric]) |
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|
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lemma (in vectorspace) mult_left_commute: |
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"x \<in> V \<Longrightarrow> a \<cdot> b \<cdot> x = b \<cdot> a \<cdot> x" |
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by (simp add: real_mult_commute mult_assoc2) |
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|
wenzelm@13515 | 257 |
lemma (in vectorspace) mult_zero_uniq: |
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"x \<in> V \<Longrightarrow> x \<noteq> 0 \<Longrightarrow> a \<cdot> x = 0 \<Longrightarrow> a = 0" |
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proof (rule classical) |
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assume a: "a \<noteq> 0" |
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assume x: "x \<in> V" "x \<noteq> 0" and ax: "a \<cdot> x = 0" |
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from x a have "x = (inverse a * a) \<cdot> x" by simp |
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also have "... = inverse a \<cdot> (a \<cdot> x)" by (rule mult_assoc) |
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also from ax have "... = inverse a \<cdot> 0" by simp |
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also have "... = 0" by simp |
bauerg@9374 | 266 |
finally have "x = 0" . |
wenzelm@10687 | 267 |
thus "a = 0" by contradiction |
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qed |
wenzelm@7917 | 269 |
|
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lemma (in vectorspace) mult_left_cancel: |
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"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> a \<noteq> 0 \<Longrightarrow> (a \<cdot> x = a \<cdot> y) = (x = y)" |
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proof |
wenzelm@13515 | 273 |
assume x: "x \<in> V" and y: "y \<in> V" and a: "a \<noteq> 0" |
wenzelm@13515 | 274 |
from x have "x = 1 \<cdot> x" by simp |
wenzelm@13515 | 275 |
also from a have "... = (inverse a * a) \<cdot> x" by simp |
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also from x have "... = inverse a \<cdot> (a \<cdot> x)" |
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by (simp only: mult_assoc) |
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also assume "a \<cdot> x = a \<cdot> y" |
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also from a y have "inverse a \<cdot> ... = y" |
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by (simp add: mult_assoc2) |
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finally show "x = y" . |
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next |
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assume "x = y" |
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then show "a \<cdot> x = a \<cdot> y" by (simp only:) |
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qed |
wenzelm@7917 | 286 |
|
wenzelm@13515 | 287 |
lemma (in vectorspace) mult_right_cancel: |
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"x \<in> V \<Longrightarrow> x \<noteq> 0 \<Longrightarrow> (a \<cdot> x = b \<cdot> x) = (a = b)" |
wenzelm@9035 | 289 |
proof |
wenzelm@13515 | 290 |
assume x: "x \<in> V" and neq: "x \<noteq> 0" |
wenzelm@13515 | 291 |
{ |
wenzelm@13515 | 292 |
from x have "(a - b) \<cdot> x = a \<cdot> x - b \<cdot> x" |
wenzelm@13515 | 293 |
by (simp add: diff_mult_distrib2) |
wenzelm@13515 | 294 |
also assume "a \<cdot> x = b \<cdot> x" |
wenzelm@13515 | 295 |
with x have "a \<cdot> x - b \<cdot> x = 0" by simp |
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finally have "(a - b) \<cdot> x = 0" . |
wenzelm@13515 | 297 |
with x neq have "a - b = 0" by (rule mult_zero_uniq) |
wenzelm@13515 | 298 |
thus "a = b" by simp |
wenzelm@13515 | 299 |
next |
wenzelm@13515 | 300 |
assume "a = b" |
wenzelm@13515 | 301 |
then show "a \<cdot> x = b \<cdot> x" by (simp only:) |
wenzelm@13515 | 302 |
} |
wenzelm@13515 | 303 |
qed |
wenzelm@7917 | 304 |
|
wenzelm@13515 | 305 |
lemma (in vectorspace) eq_diff_eq: |
wenzelm@13515 | 306 |
"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> z \<in> V \<Longrightarrow> (x = z - y) = (x + y = z)" |
wenzelm@13515 | 307 |
proof |
wenzelm@13515 | 308 |
assume x: "x \<in> V" and y: "y \<in> V" and z: "z \<in> V" |
wenzelm@13515 | 309 |
{ |
wenzelm@13515 | 310 |
assume "x = z - y" |
wenzelm@9035 | 311 |
hence "x + y = z - y + y" by simp |
wenzelm@13515 | 312 |
also from y z have "... = z + - y + y" |
wenzelm@13515 | 313 |
by (simp add: diff_eq1) |
wenzelm@10687 | 314 |
also have "... = z + (- y + y)" |
wenzelm@13515 | 315 |
by (rule add_assoc) (simp_all add: y z) |
wenzelm@13515 | 316 |
also from y z have "... = z + 0" |
wenzelm@13515 | 317 |
by (simp only: add_minus_left) |
wenzelm@13515 | 318 |
also from z have "... = z" |
wenzelm@13515 | 319 |
by (simp only: add_zero_right) |
wenzelm@13515 | 320 |
finally show "x + y = z" . |
wenzelm@9035 | 321 |
next |
wenzelm@13515 | 322 |
assume "x + y = z" |
wenzelm@9035 | 323 |
hence "z - y = (x + y) - y" by simp |
wenzelm@13515 | 324 |
also from x y have "... = x + y + - y" |
wenzelm@9035 | 325 |
by (simp add: diff_eq1) |
wenzelm@10687 | 326 |
also have "... = x + (y + - y)" |
wenzelm@13515 | 327 |
by (rule add_assoc) (simp_all add: x y) |
wenzelm@13515 | 328 |
also from x y have "... = x" by simp |
wenzelm@13515 | 329 |
finally show "x = z - y" .. |
wenzelm@13515 | 330 |
} |
wenzelm@9035 | 331 |
qed |
wenzelm@7917 | 332 |
|
wenzelm@13515 | 333 |
lemma (in vectorspace) add_minus_eq_minus: |
wenzelm@13515 | 334 |
"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> x + y = 0 \<Longrightarrow> x = - y" |
wenzelm@9035 | 335 |
proof - |
wenzelm@13515 | 336 |
assume x: "x \<in> V" and y: "y \<in> V" |
wenzelm@13515 | 337 |
from x y have "x = (- y + y) + x" by simp |
wenzelm@13515 | 338 |
also from x y have "... = - y + (x + y)" by (simp add: add_ac) |
bauerg@9374 | 339 |
also assume "x + y = 0" |
wenzelm@13515 | 340 |
also from y have "- y + 0 = - y" by simp |
wenzelm@9035 | 341 |
finally show "x = - y" . |
wenzelm@9035 | 342 |
qed |
wenzelm@7917 | 343 |
|
wenzelm@13515 | 344 |
lemma (in vectorspace) add_minus_eq: |
wenzelm@13515 | 345 |
"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> x - y = 0 \<Longrightarrow> x = y" |
wenzelm@9035 | 346 |
proof - |
wenzelm@13515 | 347 |
assume x: "x \<in> V" and y: "y \<in> V" |
bauerg@9374 | 348 |
assume "x - y = 0" |
wenzelm@13515 | 349 |
with x y have eq: "x + - y = 0" by (simp add: diff_eq1) |
wenzelm@13515 | 350 |
with _ _ have "x = - (- y)" |
wenzelm@13515 | 351 |
by (rule add_minus_eq_minus) (simp_all add: x y) |
wenzelm@13515 | 352 |
with x y show "x = y" by simp |
wenzelm@9035 | 353 |
qed |
wenzelm@7917 | 354 |
|
wenzelm@13515 | 355 |
lemma (in vectorspace) add_diff_swap: |
wenzelm@13515 | 356 |
"a \<in> V \<Longrightarrow> b \<in> V \<Longrightarrow> c \<in> V \<Longrightarrow> d \<in> V \<Longrightarrow> a + b = c + d |
wenzelm@13515 | 357 |
\<Longrightarrow> a - c = d - b" |
wenzelm@10687 | 358 |
proof - |
wenzelm@13515 | 359 |
assume vs: "a \<in> V" "b \<in> V" "c \<in> V" "d \<in> V" |
wenzelm@9035 | 360 |
and eq: "a + b = c + d" |
wenzelm@13515 | 361 |
then have "- c + (a + b) = - c + (c + d)" |
wenzelm@13515 | 362 |
by (simp add: add_left_cancel) |
wenzelm@13515 | 363 |
also have "... = d" by (rule minus_add_cancel) |
wenzelm@9035 | 364 |
finally have eq: "- c + (a + b) = d" . |
wenzelm@10687 | 365 |
from vs have "a - c = (- c + (a + b)) + - b" |
wenzelm@13515 | 366 |
by (simp add: add_ac diff_eq1) |
wenzelm@13515 | 367 |
also from vs eq have "... = d + - b" |
wenzelm@13515 | 368 |
by (simp add: add_right_cancel) |
wenzelm@13515 | 369 |
also from vs have "... = d - b" by (simp add: diff_eq2) |
wenzelm@9035 | 370 |
finally show "a - c = d - b" . |
wenzelm@9035 | 371 |
qed |
wenzelm@7917 | 372 |
|
wenzelm@13515 | 373 |
lemma (in vectorspace) vs_add_cancel_21: |
wenzelm@13515 | 374 |
"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> z \<in> V \<Longrightarrow> u \<in> V |
wenzelm@13515 | 375 |
\<Longrightarrow> (x + (y + z) = y + u) = (x + z = u)" |
wenzelm@13515 | 376 |
proof |
wenzelm@13515 | 377 |
assume vs: "x \<in> V" "y \<in> V" "z \<in> V" "u \<in> V" |
wenzelm@13515 | 378 |
{ |
wenzelm@13515 | 379 |
from vs have "x + z = - y + y + (x + z)" by simp |
wenzelm@9035 | 380 |
also have "... = - y + (y + (x + z))" |
wenzelm@13515 | 381 |
by (rule add_assoc) (simp_all add: vs) |
wenzelm@13515 | 382 |
also from vs have "y + (x + z) = x + (y + z)" |
wenzelm@13515 | 383 |
by (simp add: add_ac) |
wenzelm@13515 | 384 |
also assume "x + (y + z) = y + u" |
wenzelm@13515 | 385 |
also from vs have "- y + (y + u) = u" by simp |
wenzelm@13515 | 386 |
finally show "x + z = u" . |
wenzelm@13515 | 387 |
next |
wenzelm@13515 | 388 |
assume "x + z = u" |
wenzelm@13515 | 389 |
with vs show "x + (y + z) = y + u" |
wenzelm@13515 | 390 |
by (simp only: add_left_commute [of x]) |
wenzelm@13515 | 391 |
} |
wenzelm@9035 | 392 |
qed |
wenzelm@7917 | 393 |
|
wenzelm@13515 | 394 |
lemma (in vectorspace) add_cancel_end: |
wenzelm@13515 | 395 |
"x \<in> V \<Longrightarrow> y \<in> V \<Longrightarrow> z \<in> V \<Longrightarrow> (x + (y + z) = y) = (x = - z)" |
wenzelm@13515 | 396 |
proof |
wenzelm@13515 | 397 |
assume vs: "x \<in> V" "y \<in> V" "z \<in> V" |
wenzelm@13515 | 398 |
{ |
wenzelm@13515 | 399 |
assume "x + (y + z) = y" |
wenzelm@13515 | 400 |
with vs have "(x + z) + y = 0 + y" |
wenzelm@13515 | 401 |
by (simp add: add_ac) |
wenzelm@13515 | 402 |
with vs have "x + z = 0" |
wenzelm@13515 | 403 |
by (simp only: add_right_cancel add_closed zero) |
wenzelm@13515 | 404 |
with vs show "x = - z" by (simp add: add_minus_eq_minus) |
wenzelm@9035 | 405 |
next |
wenzelm@13515 | 406 |
assume eq: "x = - z" |
wenzelm@10687 | 407 |
hence "x + (y + z) = - z + (y + z)" by simp |
wenzelm@10687 | 408 |
also have "... = y + (- z + z)" |
wenzelm@13515 | 409 |
by (rule add_left_commute) (simp_all add: vs) |
wenzelm@13515 | 410 |
also from vs have "... = y" by simp |
wenzelm@13515 | 411 |
finally show "x + (y + z) = y" . |
wenzelm@13515 | 412 |
} |
wenzelm@9035 | 413 |
qed |
wenzelm@7917 | 414 |
|
wenzelm@10687 | 415 |
end |