**** 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.