
1 **** Isabelle93 : a faster version of Isabelle92 **** 

2 

3 Isabelle now runs faster through a combination of improvements: pattern 

4 unification, discrimination nets and removal of assumptions during 

5 simplification. A new simplifier, although less flexible than the old one, 

6 runs many times faster for large subgoals. Classical reasoning 

7 (e.g. fast_tac) runs up to 30% faster when large numbers of rules are 

8 involved. Incompatibilities are few, and mostly concern the simplifier. 

9 

10 THE SPEEDUPS 

11 

12 The new simplifier is described in the Reference Manual, Chapter 8. See 

13 below for advice on converting. 

14 

15 Pattern unification is completely invisible to users. It efficiently 

16 handles a common case of higherorder unification. 

17 

18 Discrimination nets replace the old stringtrees. They provide fast lookup 

19 in a large set of rules for matching or unification. New "net" tactics 

20 replace the "compat_..." tactics based on stringtrees. Tactics 

21 biresolve_from_nets_tac, bimatch_from_nets_tac, resolve_from_net_tac and 

22 match_from_net_tac take a net, rather than a list of rules, and perform 

23 resolution or matching. Tactics net_biresolve_tac, net_bimatch_tac 

24 net_resolve_tac and net_match_tac take a list of rules, build a net 

25 (internally) and perform resolution or matching. 

26 

27 The tactical METAHYPS, which allows a subgoal's hypotheses to be taken as a 

28 list of theorems, has been extended to handle unknowns (although not type 

29 unknowns). The simplification tactics now use METAHYPS to economise on 

30 storage consumption, and to avoid problems involving "parameters" bound in 

31 a subgoal. The modified simplifier now requires the auto_tac to take an 

32 extra argument: a list of theorems, which represents the assumptions of the 

33 current subgoal. 

34 

35 OTHER CHANGES 

36 

37 Apart from minor improvements in Pure Isabelle, the main other changes are 

38 extensions to objectlogics. HOL now contains a treatment of coinduction 

39 and corecursion, while ZF contains a formalization of equivalence classes, 

40 the integers and binary arithmetic. None of this material is documented. 

41 

42 

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

44 

45 1. Run a crude shell script to convert your MLfiles: 

46 

47 change_simp *ML 

48 

49 2. Most congruence rules are no longer needed. Hence you should remove all 

50 calls to mk_congs and mk_typed_congs (they no longer exist) and most 

51 occurrences of addcongs. The only exception are congruence rules for special 

52 constants like (in FOL) 

53 

54 [ ?P <> ?P'; ?P' ==> ?Q <> ?Q' ] ==> ?P > ?Q = ?P' > ?Q' 

55 and 

56 [ A=A'; !!x. x:A' ==> P(x) <> P'(x) ] ==> 

57 (ALL x:A. P(x)) <> (ALL x:A'. P'(x)) 

58 

59 where some of the arguments are simplified under additional premises. Most 

60 likely you don't have any constructs like that, or they are already included 

61 in the basic simpset. 

62 

63 3. In case you have used the addsplits facilities of the old simplifier: 

64 The casesplitting and simplification tactics have been separated. If you 

65 want to interleave casesplitting with simplification, you have do so 

66 explicitly by the following command: 

67 

68 ss setloop (split_tac split_thms) 

69 

70 where ss is a simpset and split_thms the list of casesplitting theorems. 

71 The shell script in step 1 tries to convert to from addsplits to setloop 

72 automatically. 

73 

74 4. If you have used setauto, you have to change it to setsolver by hand. 

75 The solver is more delicate than the auto tactic used to be. For details see 

76 the full description of the new simplifier. One very slight incompatibility 

77 is the fact that the old auto tactic could sometimes see premises as part of 

78 the proof state, whereas now they are always passed explicit as arguments. 

79 

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

81 

82 Known incompatibilities: 

83  Applying a rewrite rule cannot instantiate a subgoal. This rules out 

84 solving a premise of a conditional rewrite rule with extra unknowns by 

85 rewriting. Only the solver can instantiate. 

86 

87 Known bugs: 

88  The names of bound variables can be changed by the simplifier. 

89 

90 