* WN: eliminate "handle _ => ..." (essential for PIDE interaction):

    - either use \<^try>CARTOUCHE / \<^can>CARTOUCHE antiquotation

    - or more basic try/can combinators;

    - or more direct ML of intention;

* WN: check remaining "for tests only" wrt. \<^isac_test>CARTOUCHE;

* WN: purge BridgeLibisabelle: eliminate unused code;

* reconsider use of Thy_Info.get_theory: only works with batch-build, not within PIDE session;

* MW: ML antiqutation @{rule_thm NAME} to produce (Rule.Thm ("NAME", ThmC.numerals_to_Free "NAME"));

* MW: more concise "setup KEStore_Elems.add_rlss" etc.;

* MW: check uses of Unsynchronized.ref vs. Synchronized.var;

* MW: proper formal name space for rule set, model patterns, methods;

  proper setup command;

* MW: clarify/eliminate Isabelle/Scala add-ons (presently unused)

    diff -r /home/makarius/isabelle/repos-Isabelle2021/src/Pure/build-jars ./src/Pure/build-jars

    11a12

    >   src/Tools/isac/BridgeJEdit/isac.scala

    diff -r /home/makarius/isabelle/repos-Isabelle2021/src/Pure/Tools/scala_project.scala ./src/Pure/Tools/scala_project.scala

    76a77

    >       "src/Tools/isac/etc" -> Path.explode("isabelle.isac"),

* WN: more direct logical foundations wrt. Isabelle/HOL, eliminate many axiomatizations

    - quite often "axiomatization ..." can be turned into "lemma ... by auto"

      without further ado;

    - sometimes this requires to use more specific types / type classes;

    - sometimes this requires to use proper definitional mechanisms (e.g. 'primrec', 'fun');

    - a few "hard" cases will remain, to be reconsidered eventually (e.g. differentiation);

    - abbreviation real_powr :: "real \<Rightarrow> real \<Rightarrow> real"  (infixr "\<up>" 80)

      where "x \<up> a \<equiv> x powr a"

* WN: eliminate ThmC.numerals_to_Free, use existing Isabelle/HOL representation

    - clarify role of type "real" vs. "float" (see theory "HOL-Library.Float");

* WN: investigate errors further which popped up in rewriting when replacing ^^^ by \<up> in ac7426ab0491.

      The errors occur with examples in test/../poly.sml, which do not work properly in isabisac20 either.

* WN: cleanup remaining ^^^ in comments (but sometimes it is just ASCII art);

* WN: simplify const names like "is'_expanded": no need to imitate the escape of mixfix syntax;

* WN: proper statement for rcancel_den ("not" is a free variable!?!!):

    rcancel_den:             "not(a=0) ==> a * (b / a) = b" and

* WN: "fun pr_ord" is not required if used with @{make_string}, @{print}, @{print tracing};

* WN: use File.read / File.write instead of low-level TextIO operations (not portable);

* WN: use Path.T (e.g. via Path.explode) for portability;

* WN: refrain from using global /tmp directory

  (e.g. see Isabelle_System.create_tmp_path / with_tmp_file / with_tmp_dir);