Christian Wirth wrote: > i have a conditon NOT(pred(A)) and a fact pred(1). The existenc check > \+(\+(not(pred(A))) should succeed, because it's possible that A is not > bound to 1, but it fails because A gets bound to 1 by the test. > How can i test if a NOT(condition) is solvable ? > Hi Christian, not/1 and \+/1 behave exactly the same -- I believe \+/1 was added because not/1 does not do negation as some people understand it, so \+/2 is considered by some to be a better name for the way Prolog (and thus ECLiPSe) implements negation. Specifically, negation as failure (with closed world assumption). \+(A) and not(A) succeeds if A fails, and fails if A succeeds. Thus \+( \+( not(A))) (which is what you have) has exactly the same semantics as \+(A) (and not(A)), except it does more work. What exact semantics do you want? Note that if you want pred(A) to behave like a constraint (i.e. it can delay if it is not immediately entailed), then you cannot use the \+(\+(A)) trick, because if A delays, A will appear to succeed, and \+(A) will fail. Cheers, Kish -- This e-mail may contain confidential and privileged material for the sole use of the intended recipient. Any review, use, distribution or disclosure by others is strictly prohibited. If you are not the intended recipient (or authorized to receive for the recipient), please contact the sender by reply e-mail and delete all copies of this message. Cisco Systems Limited (Company Number: 02558939), is registered in England and Wales with its registered office at 1 Callaghan Square, Cardiff, South Glamorgan CF10 5BT.Received on Wed Apr 14 2010 - 17:50:50 CEST
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