doc-src/CHANGES-93.txt
author clasohm
Tue, 09 May 1995 10:42:23 +0200
changeset 1112 737a1a0df754
parent 103 30bd42401ab2
permissions -rw-r--r--
added \CHOL

**** Isabelle-93 : 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.  A new simplifier, although less flexible than the old one,
runs many times faster for large subgoals.  Classical reasoning
(e.g. fast_tac) runs up to 30% faster when large numbers of rules are
involved.  Incompatibilities are few, and mostly concern the simplifier.

THE SPEEDUPS

The new simplifier is described in the Reference Manual, Chapter 8.  See
below for advice on converting.

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.


CONVERTING FROM THE OLD TO THE NEW SIMPLIFIER (for FOL/ZF/LCF/HOL)

1.  Run a crude shell script to convert your ML-files:

	change_simp *ML

2.  Most congruence rules are no longer needed.  Hence you should remove all
calls to mk_congs and mk_typed_congs (they no longer exist) and most
occurrences of addcongs.  The only exception are congruence rules for special
constants like (in FOL)

[| ?P <-> ?P'; ?P' ==> ?Q <-> ?Q' |] ==> ?P --> ?Q = ?P' --> ?Q'
and 
[| A=A';  !!x. x:A' ==> P(x) <-> P'(x) |] ==>
(ALL x:A. P(x)) <-> (ALL x:A'. P'(x))

where some of the arguments are simplified under additional premises.  Most
likely you don't have any constructs like that, or they are already included
in the basic simpset.

3.  In case you have used the addsplits facilities of the old simplifier:
The case-splitting and simplification tactics have been separated.  If you
want to interleave case-splitting with simplification, you have do so
explicitly by the following command:

ss setloop (split_tac split_thms)

where ss is a simpset and split_thms the list of case-splitting theorems.
The shell script in step 1 tries to convert to from addsplits to setloop
automatically.

4.  If you have used setauto, you have to change it to setsolver by hand.
The solver is more delicate than the auto tactic used to be.  For details see
the full description of the new simplifier.  One very slight incompatibility
is the fact that the old auto tactic could sometimes see premises as part of
the proof state, whereas now they are always passed explicit as arguments.

5.  It is quite likely that a few proofs require further hand massaging.

Known incompatibilities:
- Applying a rewrite rule cannot instantiate a subgoal.  This rules out
solving a premise of a conditional rewrite rule with extra unknowns by
rewriting.  Only the solver can instantiate.

Known bugs:
- The names of bound variables can be changed by the simplifier.