Release notes for HOL4, Trindemossen-2

(Released: 12 August 2025)

We are pleased to announce the Trindemossen-2 release of HOL4.

Contents

• New features
• Bugs fixed
• New theories
• New tools
• New examples
• Incompatibilities

New features:

• We now support (and recommend) a new header syntax for Script.sml files. Instead of the existing boilerplate (open HolKernel … val _ = new_theory…), users write something like

     Theory foo
     Ancestors real_topology …
     Libs realLib
  

  to begin their files. This syntax and its options are documented in a new chapter of the DESCRIPTION manual. Thanks to Mario Carneiro and Daniel Nezamabadi for the work done implementing this, and then converting all the script files in src to use this syntax.

• The simplifier now supports NoAsms and IgnAsm special forms that allow all assumptions (or those matching the provided pattern, in the case of IgnAsm) to be excluded. See the DESCRIPTION and REFERENCE manuals for details. (GitHub issue)

• The automatic termination-finding technology behind Definition (and lower-level APIs) is now rather stronger, especially when dealing with higher order recursions using list operators. This should reduce the number of times you need to introduce explicit Termination-argument blocks to accompany your definitions. Termination condition extraction and termination relation guessing now have traces (“Definition.TC extraction” and “Definition.termination candidates”) that can be examined for illumination. See src/tfl/examples/termination_proverScript.sml for examples.

• All of HOL’s internal files are now stored in/under one sub-directory of the source directory where user *Script.sml files are found. Previously, HOL used .HOLMK, .holobjs, and .hollogs. Now everything is stored in/under the sub-directory .hol.

  To get rid of old directories, which are now just going to be useless clutter, shell command-lines such as

     find . -path '*/.hollogs/*' -delete
     find . -name '.hollogs' -delete

  might be used from the root of your HOL development. Alternatively, use Holmake -r cleanAll with your old HOL version, and then switch.

• Under Poly/ML, the hol and hol.bare executables can be passed the –-noconfig command-line flag to stop them consulting user config files in the user’s home directory (these have names like hol-config.sml). Under both Moscow ML and Poly/ML, configuration files are also ignored if there is a HOL_NOCONFIG environment variable set.

• oneline from bossLib now supports one-line-ification of mutually recrusive functions. Each function becomes an equation of its own in the theorem returned by oneline.

• The Poly/ML implementation now offers a -z (or --zero) command-line option to make the NUL byte be the end-marker for strings being sent to the compiler. Otherwise, the compiler makes a best effort guess about when it should interact based on the presence of semi-colons.

Bugs fixed:

• EVERY_CASE_TAC would loop if the “split-upon” subterm was already an assumption, but no longer.

New theories:

• number, combinatorics and prime: These theories combine material from examples/algebra/lib, etc. They contain some more advanced results from number theory (in particular properties of prime numbers) and combinatorics.

• monoid, group, ring and real_algebra: These theories combine material previously held in examples/algebra. A monoid is an algebraic structure: with a carrier set, a binary operation and an identity element. A group is an algebraic structure: a monoid with all its elements invertible. A ring takes into account the interplay between its additive group and multiplicative monoid.

New tools:

• Tactic.TRANS_TAC (ported from HOL-Light) applies transitivity theorem to goal with chosen intermediate term. See its DOC for more details.

• intLib.INTEGER_TAC and intLib.INTEGER_RULE (ported from HOL-Light): simple decision procedures for equations of multivariate polynomials of integers, and simple equations about divisibility of integers.

• last_assume_tac has been added. It is the same as assume_tac except it adds the new assumption to the top of the list of assumptions instead of the bottom.

New examples:

• Dijkstra’s algorithm for computing shortest paths: examples/algorithms/dijkstraScript.sml

Incompatibilities:

• numLib.prefer_num has been renamed to numLib.temp_prefer_num, which name better describes its semantics. The prefer_num entry-point is now used to make a change “permanent” (again following the naming convention used by many parsing-related entry-points), which is to say that the overloads made by this function will be exported to child theories.

• The cv translator’s entry points with _pre now take a new string argument, e.g., what used to be cv_trans_pre foo_def is now cv_trans_pre "foo_pre" foo_def. Mutually recursive functions require a name for each functions. In the string argument, multiple names are given either with spaces separating them, e.g., "foo_pre foo_list_pre", or commas separating them, e.g., "foo_pre,foo_list_pre" or "foo_pre, foo_list_pre". The old behaviour (inventing names) is supported by passing the empty string "" as the name, i.e., cv_trans_pre "" foo_def.

• Editor mode implementations have moved in the HOL sources to tools/editor-modes/{editor-name}. This may affect editor initialisations/configurations, particularly if they hard-code a reference to a particular path. For example, in the recommended setup for emacs, users will need to change

     (load "<path>/HOL/tools/hol-mode")
     (load "<path>/HOL/tools/hol-unicode")

  to

     (load "<path>/HOL/tools/editor-modes/emacs/hol-mode")
     (load "<path>/HOL/tools/editor-modes/emacs/hol-unicode")

• The types of DB.find and DB.match have changed so that instead of returning

     (string * string) * (thm * class)

  they now return

     (string * string) * (thm * class * thm_src_location)

  Using the #1 o #2 selector should be future-proof here.

• util_probTheory has been merged into sigma_algebraTheory.

• In set_relationTheory, the constant tc has been renamed to transitive_closure.

• Various adjoin_to… entry-points in Theory have been removed. The biggest incompatibility this causes is the removal of the <thy>_grammars binding from all <thy>Theory structures. To access the grammars specific to a particular theory (foo, say), one must now write

     valOf $ Parse.grammarDB {thyname="foo"}

  where the call may fail if the theory is not present in the hierarchy.

• ASSUME_NAMED_TAC now puts the new named assumption at the top of the assumption list, but below the other named assumptions. Previously, named assumptions were added to the bottom of the assumption list (where they might get in the way).

• Selecting numbered options in the Moscow ML HOL help system now requires the number choice to be followed by semicolon-newline instead of just a newline character.