make proofs work whether or not One_nat_def is a simp rule; replace 1 with Suc 0 in the rhs of some simp rules
1 (* Title: HOL/Power.thy
3 Author: Lawrence C Paulson, Cambridge University Computer Laboratory
4 Copyright 1997 University of Cambridge
8 header{*Exponentiation*}
15 fixes power :: "'a \<Rightarrow> nat \<Rightarrow> 'a" (infixr "^" 80)
17 subsection{*Powers for Arbitrary Monoids*}
19 class recpower = monoid_mult + power +
20 assumes power_0 [simp]: "a ^ 0 = 1"
21 assumes power_Suc: "a ^ Suc n = a * (a ^ n)"
23 lemma power_0_Suc [simp]: "(0::'a::{recpower,semiring_0}) ^ (Suc n) = 0"
24 by (simp add: power_Suc)
26 text{*It looks plausible as a simprule, but its effect can be strange.*}
27 lemma power_0_left: "0^n = (if n=0 then 1 else (0::'a::{recpower,semiring_0}))"
28 by (induct n) simp_all
30 lemma power_one [simp]: "1^n = (1::'a::recpower)"
31 by (induct n) (simp_all add: power_Suc)
33 lemma power_one_right [simp]: "(a::'a::recpower) ^ 1 = a"
34 unfolding One_nat_def by (simp add: power_Suc)
36 lemma power_commutes: "(a::'a::recpower) ^ n * a = a * a ^ n"
37 by (induct n) (simp_all add: power_Suc mult_assoc)
39 lemma power_Suc2: "(a::'a::recpower) ^ Suc n = a ^ n * a"
40 by (simp add: power_Suc power_commutes)
42 lemma power_add: "(a::'a::recpower) ^ (m+n) = (a^m) * (a^n)"
43 by (induct m) (simp_all add: power_Suc mult_ac)
45 lemma power_mult: "(a::'a::recpower) ^ (m*n) = (a^m) ^ n"
46 by (induct n) (simp_all add: power_Suc power_add)
48 lemma power_mult_distrib: "((a::'a::{recpower,comm_monoid_mult}) * b) ^ n = (a^n) * (b^n)"
49 by (induct n) (simp_all add: power_Suc mult_ac)
51 lemma zero_less_power[simp]:
52 "0 < (a::'a::{ordered_semidom,recpower}) ==> 0 < a^n"
54 apply (simp_all add: power_Suc zero_less_one mult_pos_pos)
57 lemma zero_le_power[simp]:
58 "0 \<le> (a::'a::{ordered_semidom,recpower}) ==> 0 \<le> a^n"
59 apply (simp add: order_le_less)
61 apply (simp_all add: zero_less_one power_0_left)
64 lemma one_le_power[simp]:
65 "1 \<le> (a::'a::{ordered_semidom,recpower}) ==> 1 \<le> a^n"
67 apply (simp_all add: power_Suc)
68 apply (rule order_trans [OF _ mult_mono [of 1 _ 1]])
69 apply (simp_all add: zero_le_one order_trans [OF zero_le_one])
72 lemma gt1_imp_ge0: "1 < a ==> 0 \<le> (a::'a::ordered_semidom)"
73 by (simp add: order_trans [OF zero_le_one order_less_imp_le])
75 lemma power_gt1_lemma:
76 assumes gt1: "1 < (a::'a::{ordered_semidom,recpower})"
79 have "1*1 < a*1" using gt1 by simp
80 also have "\<dots> \<le> a * a^n" using gt1
81 by (simp only: mult_mono gt1_imp_ge0 one_le_power order_less_imp_le
82 zero_le_one order_refl)
83 finally show ?thesis by simp
86 lemma one_less_power[simp]:
87 "\<lbrakk>1 < (a::'a::{ordered_semidom,recpower}); 0 < n\<rbrakk> \<Longrightarrow> 1 < a ^ n"
88 by (cases n, simp_all add: power_gt1_lemma power_Suc)
91 "1 < (a::'a::{ordered_semidom,recpower}) ==> 1 < a ^ (Suc n)"
92 by (simp add: power_gt1_lemma power_Suc)
94 lemma power_le_imp_le_exp:
95 assumes gt1: "(1::'a::{recpower,ordered_semidom}) < a"
96 shows "!!n. a^m \<le> a^n ==> m \<le> n"
105 from prems have "a * a^m \<le> 1" by (simp add: power_Suc)
106 with gt1 show ?thesis
107 by (force simp only: power_gt1_lemma
108 linorder_not_less [symmetric])
111 from prems show ?thesis
112 by (force dest: mult_left_le_imp_le
113 simp add: power_Suc order_less_trans [OF zero_less_one gt1])
117 text{*Surely we can strengthen this? It holds for @{text "0<a<1"} too.*}
118 lemma power_inject_exp [simp]:
119 "1 < (a::'a::{ordered_semidom,recpower}) ==> (a^m = a^n) = (m=n)"
120 by (force simp add: order_antisym power_le_imp_le_exp)
122 text{*Can relax the first premise to @{term "0<a"} in the case of the
124 lemma power_less_imp_less_exp:
125 "[| (1::'a::{recpower,ordered_semidom}) < a; a^m < a^n |] ==> m < n"
126 by (simp add: order_less_le [of m n] order_less_le [of "a^m" "a^n"]
131 "[|a \<le> b; (0::'a::{recpower,ordered_semidom}) \<le> a|] ==> a^n \<le> b^n"
133 apply (simp_all add: power_Suc)
134 apply (auto intro: mult_mono order_trans [of 0 a b])
137 lemma power_strict_mono [rule_format]:
138 "[|a < b; (0::'a::{recpower,ordered_semidom}) \<le> a|]
139 ==> 0 < n --> a^n < b^n"
141 apply (auto simp add: mult_strict_mono power_Suc
142 order_le_less_trans [of 0 a b])
145 lemma power_eq_0_iff [simp]:
146 "(a^n = 0) \<longleftrightarrow>
147 (a = (0::'a::{mult_zero,zero_neq_one,no_zero_divisors,recpower}) & n\<noteq>0)"
149 apply (auto simp add: power_Suc zero_neq_one [THEN not_sym] no_zero_divisors)
153 lemma field_power_not_zero:
154 "a \<noteq> (0::'a::{ring_1_no_zero_divisors,recpower}) ==> a^n \<noteq> 0"
157 lemma nonzero_power_inverse:
158 fixes a :: "'a::{division_ring,recpower}"
159 shows "a \<noteq> 0 ==> inverse (a ^ n) = (inverse a) ^ n"
161 apply (auto simp add: power_Suc nonzero_inverse_mult_distrib power_commutes)
162 done (* TODO: reorient or rename to nonzero_inverse_power *)
164 text{*Perhaps these should be simprules.*}
166 fixes a :: "'a::{division_ring,division_by_zero,recpower}"
167 shows "inverse (a ^ n) = (inverse a) ^ n"
168 apply (cases "a = 0")
169 apply (simp add: power_0_left)
170 apply (simp add: nonzero_power_inverse)
171 done (* TODO: reorient or rename to inverse_power *)
173 lemma power_one_over: "1 / (a::'a::{field,division_by_zero,recpower})^n =
175 apply (simp add: divide_inverse)
176 apply (rule power_inverse)
179 lemma nonzero_power_divide:
180 "b \<noteq> 0 ==> (a/b) ^ n = ((a::'a::{field,recpower}) ^ n) / (b ^ n)"
181 by (simp add: divide_inverse power_mult_distrib nonzero_power_inverse)
184 "(a/b) ^ n = ((a::'a::{field,division_by_zero,recpower}) ^ n / b ^ n)"
185 apply (case_tac "b=0", simp add: power_0_left)
186 apply (rule nonzero_power_divide)
190 lemma power_abs: "abs(a ^ n) = abs(a::'a::{ordered_idom,recpower}) ^ n"
192 apply (auto simp add: power_Suc abs_mult)
195 lemma zero_less_power_abs_iff [simp,noatp]:
196 "(0 < (abs a)^n) = (a \<noteq> (0::'a::{ordered_idom,recpower}) | n=0)"
199 show ?case by (simp add: zero_less_one)
202 show ?case by (auto simp add: prems power_Suc zero_less_mult_iff
206 lemma zero_le_power_abs [simp]:
207 "(0::'a::{ordered_idom,recpower}) \<le> (abs a)^n"
208 by (rule zero_le_power [OF abs_ge_zero])
210 lemma power_minus: "(-a) ^ n = (- 1)^n * (a::'a::{ring_1,recpower}) ^ n"
212 case 0 show ?case by simp
214 case (Suc n) then show ?case
215 by (simp add: power_Suc2 mult_assoc)
218 text{*Lemma for @{text power_strict_decreasing}*}
219 lemma power_Suc_less:
220 "[|(0::'a::{ordered_semidom,recpower}) < a; a < 1|]
223 apply (auto simp add: power_Suc mult_strict_left_mono)
226 lemma power_strict_decreasing:
227 "[|n < N; 0 < a; a < (1::'a::{ordered_semidom,recpower})|]
231 apply (auto simp add: power_Suc power_Suc_less less_Suc_eq)
233 apply (subgoal_tac "a * a^m < 1 * a^n", simp)
234 apply (rule mult_strict_mono)
235 apply (auto simp add: zero_less_one order_less_imp_le)
238 text{*Proof resembles that of @{text power_strict_decreasing}*}
239 lemma power_decreasing:
240 "[|n \<le> N; 0 \<le> a; a \<le> (1::'a::{ordered_semidom,recpower})|]
244 apply (auto simp add: power_Suc le_Suc_eq)
246 apply (subgoal_tac "a * a^m \<le> 1 * a^n", simp)
247 apply (rule mult_mono)
248 apply (auto simp add: zero_le_one)
251 lemma power_Suc_less_one:
252 "[| 0 < a; a < (1::'a::{ordered_semidom,recpower}) |] ==> a ^ Suc n < 1"
253 apply (insert power_strict_decreasing [of 0 "Suc n" a], simp)
256 text{*Proof again resembles that of @{text power_strict_decreasing}*}
257 lemma power_increasing:
258 "[|n \<le> N; (1::'a::{ordered_semidom,recpower}) \<le> a|] ==> a^n \<le> a^N"
261 apply (auto simp add: power_Suc le_Suc_eq)
263 apply (subgoal_tac "1 * a^n \<le> a * a^m", simp)
264 apply (rule mult_mono)
265 apply (auto simp add: order_trans [OF zero_le_one])
268 text{*Lemma for @{text power_strict_increasing}*}
269 lemma power_less_power_Suc:
270 "(1::'a::{ordered_semidom,recpower}) < a ==> a^n < a * a^n"
272 apply (auto simp add: power_Suc mult_strict_left_mono order_less_trans [OF zero_less_one])
275 lemma power_strict_increasing:
276 "[|n < N; (1::'a::{ordered_semidom,recpower}) < a|] ==> a^n < a^N"
279 apply (auto simp add: power_less_power_Suc power_Suc less_Suc_eq)
281 apply (subgoal_tac "1 * a^n < a * a^m", simp)
282 apply (rule mult_strict_mono)
283 apply (auto simp add: order_less_trans [OF zero_less_one] order_less_imp_le)
286 lemma power_increasing_iff [simp]:
287 "1 < (b::'a::{ordered_semidom,recpower}) ==> (b ^ x \<le> b ^ y) = (x \<le> y)"
288 by (blast intro: power_le_imp_le_exp power_increasing order_less_imp_le)
290 lemma power_strict_increasing_iff [simp]:
291 "1 < (b::'a::{ordered_semidom,recpower}) ==> (b ^ x < b ^ y) = (x < y)"
292 by (blast intro: power_less_imp_less_exp power_strict_increasing)
294 lemma power_le_imp_le_base:
295 assumes le: "a ^ Suc n \<le> b ^ Suc n"
296 and ynonneg: "(0::'a::{ordered_semidom,recpower}) \<le> b"
300 then have "b < a" by (simp only: linorder_not_le)
301 then have "b ^ Suc n < a ^ Suc n"
302 by (simp only: prems power_strict_mono)
303 from le and this show "False"
304 by (simp add: linorder_not_less [symmetric])
307 lemma power_less_imp_less_base:
308 fixes a b :: "'a::{ordered_semidom,recpower}"
309 assumes less: "a ^ n < b ^ n"
310 assumes nonneg: "0 \<le> b"
312 proof (rule contrapos_pp [OF less])
314 hence "b \<le> a" by (simp only: linorder_not_less)
315 hence "b ^ n \<le> a ^ n" using nonneg by (rule power_mono)
316 thus "~ a ^ n < b ^ n" by (simp only: linorder_not_less)
319 lemma power_inject_base:
320 "[| a ^ Suc n = b ^ Suc n; 0 \<le> a; 0 \<le> b |]
321 ==> a = (b::'a::{ordered_semidom,recpower})"
322 by (blast intro: power_le_imp_le_base order_antisym order_eq_refl sym)
324 lemma power_eq_imp_eq_base:
325 fixes a b :: "'a::{ordered_semidom,recpower}"
326 shows "\<lbrakk>a ^ n = b ^ n; 0 \<le> a; 0 \<le> b; 0 < n\<rbrakk> \<Longrightarrow> a = b"
327 by (cases n, simp_all, rule power_inject_base)
329 text {* The divides relation *}
331 lemma le_imp_power_dvd:
332 fixes a :: "'a::{comm_semiring_1,recpower}"
333 assumes "m \<le> n" shows "a^m dvd a^n"
335 have "a^n = a^(m + (n - m))"
336 using `m \<le> n` by simp
337 also have "\<dots> = a^m * a^(n - m)"
339 finally show "a^n = a^m * a^(n - m)" .
343 fixes a b :: "'a::{comm_semiring_1,recpower}"
344 shows "a^n dvd b \<Longrightarrow> m \<le> n \<Longrightarrow> a^m dvd b"
345 by (rule dvd_trans [OF le_imp_power_dvd])
348 subsection{*Exponentiation for the Natural Numbers*}
350 instantiation nat :: recpower
353 primrec power_nat where
354 "p ^ 0 = (1\<Colon>nat)"
355 | "p ^ (Suc n) = (p\<Colon>nat) * (p ^ n)"
359 show "z^0 = 1" by simp
360 show "z^(Suc n) = z * (z^n)" by simp
366 "of_nat (m ^ n) = (of_nat m::'a::{semiring_1,recpower}) ^ n"
367 by (induct n, simp_all add: power_Suc of_nat_mult)
369 lemma nat_one_le_power [simp]: "Suc 0 \<le> i ==> Suc 0 \<le> i^n"
370 by (rule one_le_power [of i n, unfolded One_nat_def])
372 lemma nat_zero_less_power_iff [simp]: "(x^n > 0) = (x > (0::nat) | n=0)"
373 by (induct "n", auto)
375 lemma nat_power_eq_Suc_0_iff [simp]:
376 "((x::nat)^m = Suc 0) = (m = 0 | x = Suc 0)"
377 by (induct_tac m, auto)
379 lemma power_Suc_0[simp]: "(Suc 0)^n = Suc 0"
382 text{*Valid for the naturals, but what if @{text"0<i<1"}?
383 Premises cannot be weakened: consider the case where @{term "i=0"},
384 @{term "m=1"} and @{term "n=0"}.*}
385 lemma nat_power_less_imp_less:
386 assumes nonneg: "0 < (i\<Colon>nat)"
387 assumes less: "i^m < i^n"
389 proof (cases "i = 1")
390 case True with less power_one [where 'a = nat] show ?thesis by simp
392 case False with nonneg have "1 < i" by auto
393 from power_strict_increasing_iff [OF this] less show ?thesis ..
398 shows "n <= m ==> (a::'a::{recpower, field}) ^ (m-n) = (a^m) / (a^n)"
399 by (induct m n rule: diff_induct)
400 (simp_all add: power_Suc nonzero_mult_divide_cancel_left nz)
403 text{*ML bindings for the general exponentiation theorems*}
406 val power_0 = thm"power_0";
407 val power_Suc = thm"power_Suc";
408 val power_0_Suc = thm"power_0_Suc";
409 val power_0_left = thm"power_0_left";
410 val power_one = thm"power_one";
411 val power_one_right = thm"power_one_right";
412 val power_add = thm"power_add";
413 val power_mult = thm"power_mult";
414 val power_mult_distrib = thm"power_mult_distrib";
415 val zero_less_power = thm"zero_less_power";
416 val zero_le_power = thm"zero_le_power";
417 val one_le_power = thm"one_le_power";
418 val gt1_imp_ge0 = thm"gt1_imp_ge0";
419 val power_gt1_lemma = thm"power_gt1_lemma";
420 val power_gt1 = thm"power_gt1";
421 val power_le_imp_le_exp = thm"power_le_imp_le_exp";
422 val power_inject_exp = thm"power_inject_exp";
423 val power_less_imp_less_exp = thm"power_less_imp_less_exp";
424 val power_mono = thm"power_mono";
425 val power_strict_mono = thm"power_strict_mono";
426 val power_eq_0_iff = thm"power_eq_0_iff";
427 val field_power_eq_0_iff = thm"power_eq_0_iff";
428 val field_power_not_zero = thm"field_power_not_zero";
429 val power_inverse = thm"power_inverse";
430 val nonzero_power_divide = thm"nonzero_power_divide";
431 val power_divide = thm"power_divide";
432 val power_abs = thm"power_abs";
433 val zero_less_power_abs_iff = thm"zero_less_power_abs_iff";
434 val zero_le_power_abs = thm "zero_le_power_abs";
435 val power_minus = thm"power_minus";
436 val power_Suc_less = thm"power_Suc_less";
437 val power_strict_decreasing = thm"power_strict_decreasing";
438 val power_decreasing = thm"power_decreasing";
439 val power_Suc_less_one = thm"power_Suc_less_one";
440 val power_increasing = thm"power_increasing";
441 val power_strict_increasing = thm"power_strict_increasing";
442 val power_le_imp_le_base = thm"power_le_imp_le_base";
443 val power_inject_base = thm"power_inject_base";
446 text{*ML bindings for the remaining theorems*}
449 val nat_one_le_power = thm"nat_one_le_power";
450 val nat_power_less_imp_less = thm"nat_power_less_imp_less";
451 val nat_zero_less_power_iff = thm"nat_zero_less_power_iff";