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

  + consider in Build_Thydata:  Thy_Hierarchy.insert_errpatIDs

  + consider in Biegelinie.thy: KEStore_Elems.add_thes, 

* 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"),

* MW: when Isabelle inner syntax is processed literally in Isabelle/ML, prefer formal Input.source

with literal \<open>...\<close> instead of old-fashioned "..."; this will eventually allow automated update of

old ASCII notation (e.g. "EX" vs. "\<exists>"), with the help of PIDE markup;

* Is it possible to eliminate union_overwrite, in favour of more standard data

  add/merge discipline?

* What is the purpose of "#numeral" instead of plain numeral?

* Check/clarify Context.theory_name vs. Context.theory_long_name.

* WN: remove always empty arguments in MethodC.prep_input and Problem.prep_input

  (following the "TODO" comment);

* WN: eliminate ThyC.to_ctxt, use Proof_Context.init_global inline to make more

  clear where the normal Isabelle context-discipline is bypassed;

* WN: standardize theory for KEStore_Elems.add_rlss, KEStore_Elems.add_mets, KEStore_Elems.add_pbts

    - should be always the current @{theory} of the enclosing "setup" command;

    - avoid old-style "val thy = @{theory}" somewhere in a theory file;

* 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);

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

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

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

      Left ^^^ in doc-isac (old master-theses, etc: "x^^^#2 + #8" ... # are left, too)

      Left "ASCII art" in case of indicating comments pointing at facts ABOVE.

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