53 lines
1.1 KiB
Perl
53 lines
1.1 KiB
Perl
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% PATH CONSISTENCY, simple
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% thom fruehwirth ECRC 941201, simplified version of time-pc.chr
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% 980311 Thom Fruehwirth, LMU, adapted to Sicstus CHR
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:- use_module(library(chr)).
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handler path.
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option(already_in_heads,on).
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constraints con/3.
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% con(X,Y,C) means that constraint C holds between variables X and Y
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intersect_xy_xy @ con(X, Y, C1), con(X, Y, C2) <=>
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inter(C1, C2, C3),
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con(X,Y,C3).
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intersect_xy_yx @ con(X, Y, C1), con(Y, X, CR) <=>
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invert(CR, C2),
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inter(C1, C2, C3),
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con(X,Y,C3).
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propagate_xy_yz @ con(X, Y, C1), con(Y, Z, C2) ==>
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trans(C1, C2, C3)
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con(X, Z, C3).
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propagate_xy_xz @ con(X, Y, CR), con(X, Z, C2) ==>
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invert(CR,C1),
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trans(C1, C2, C3)
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con(Y, Z, C3).
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propagate_xy_zy @ con(X, Y, C1), con(Z, Y, CR) ==>
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invert(CR,C2),
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trans(C1, C2, C3)
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con(X, Z, C3).
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% Example ---------------------------------
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% constraints are < and >
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invert(<,>).
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invert(>,<).
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% fail if empty constraint would be produced
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inter(C,C,C).
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% fail if most general constraint would be produced
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trans(C,C,C).
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% ?- con(A,B,>),con(A,C,>),con(B,D,>),con(C,D,>).
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/*--------------- eof path.pl ----------------------------------------------*/
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