CHANGES-92f.txt
author paulson
Sat, 08 Feb 2003 16:05:33 +0100
changeset 13812 91713a1915ee
parent 0 a5a9c433f639
permissions -rw-r--r--
converting HOL/UNITY to use unconditional fairness

**** Isabelle-92f : a faster version of Isabelle-92 ****

Isabelle now runs faster through a combination of improvements: pattern
unification, discrimination nets and removal of assumptions during
simplification.  Classical reasoning (e.g. fast_tac) runs up to 30% faster
when large numbers of rules are involved.  Rewriting (e.g. SIMP_TAC) runs
up to 3 times faster for large subgoals.  

The new version will not benefit everybody; unless you require greater
speed, it may be best to stay with the existing version.  The new changes
have not been documented properly, and there are a few incompatibilities.

THE SPEEDUPS

Pattern unification is completely invisible to users.  It efficiently
handles a common case of higher-order unification.

Discrimination nets replace the old stringtrees.  They provide fast lookup
in a large set of rules for matching or unification.  New "net" tactics
replace the "compat_..." tactics based on stringtrees.  Tactics
biresolve_from_nets_tac, bimatch_from_nets_tac, resolve_from_net_tac and
match_from_net_tac take a net, rather than a list of rules, and perform
resolution or matching.  Tactics net_biresolve_tac, net_bimatch_tac
net_resolve_tac and net_match_tac take a list of rules, build a net
(internally) and perform resolution or matching.

The tactical METAHYPS, which allows a subgoal's hypotheses to be taken as a
list of theorems, has been extended to handle unknowns (although not type
unknowns).  The simplification tactics now use METAHYPS to economise on
storage consumption, and to avoid problems involving "parameters" bound in
a subgoal.  The modified simplifier now requires the auto_tac to take an
extra argument: a list of theorems, which represents the assumptions of the
current subgoal.

OTHER CHANGES

Apart from minor improvements in Pure Isabelle, the main other changes are
extensions to object-logics.  HOL now contains a treatment of co-induction
and co-recursion, while ZF contains a formalization of equivalence classes,
the integers and binary arithmetic.  None of this material is documented.