CHANGES-92f.txt
author wenzelm
Tue, 22 Jul 1997 19:33:30 +0200
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**** Isabelle-92f : a faster version of Isabelle-92 ****
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Isabelle now runs faster through a combination of improvements: pattern
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unification, discrimination nets and removal of assumptions during
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simplification.  Classical reasoning (e.g. fast_tac) runs up to 30% faster
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when large numbers of rules are involved.  Rewriting (e.g. SIMP_TAC) runs
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up to 3 times faster for large subgoals.  
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The new version will not benefit everybody; unless you require greater
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speed, it may be best to stay with the existing version.  The new changes
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have not been documented properly, and there are a few incompatibilities.
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THE SPEEDUPS
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Pattern unification is completely invisible to users.  It efficiently
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handles a common case of higher-order unification.
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Discrimination nets replace the old stringtrees.  They provide fast lookup
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in a large set of rules for matching or unification.  New "net" tactics
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replace the "compat_..." tactics based on stringtrees.  Tactics
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biresolve_from_nets_tac, bimatch_from_nets_tac, resolve_from_net_tac and
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match_from_net_tac take a net, rather than a list of rules, and perform
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resolution or matching.  Tactics net_biresolve_tac, net_bimatch_tac
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net_resolve_tac and net_match_tac take a list of rules, build a net
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(internally) and perform resolution or matching.
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The tactical METAHYPS, which allows a subgoal's hypotheses to be taken as a
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list of theorems, has been extended to handle unknowns (although not type
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unknowns).  The simplification tactics now use METAHYPS to economise on
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storage consumption, and to avoid problems involving "parameters" bound in
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a subgoal.  The modified simplifier now requires the auto_tac to take an
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extra argument: a list of theorems, which represents the assumptions of the
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current subgoal.
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OTHER CHANGES
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Apart from minor improvements in Pure Isabelle, the main other changes are
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extensions to object-logics.  HOL now contains a treatment of co-induction
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and co-recursion, while ZF contains a formalization of equivalence classes,
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the integers and binary arithmetic.  None of this material is documented.