Zero-effect clauses

Note that writing clauses like

p(1,2) :- false.

has absolutely no effect on the meaning of Prolog program - you might as well leave them out (because everything that is left out is considered false - Closed World Assumption)

For example:

p(2,4) :- false.
p(A,B) :- between(1,4,A),B is 2*A.

Result:

?- p(2,4).
true.

?- bagof([X,Y],p(X,Y),Bag).
Bag = [[1, 2], [2, 4], [3, 6], [4, 8]].

and it is exactly the same for

p(A,B) :- between(1,4,A),B is 2*A.
p(2,4) :- false.

or

p(A,B) :- between(1,4,A),B is 2*A.

And now for some inconsistency

Using false and the cut means you can write Bad and Inconsistent Programs:

f(X,X) :- !, false.
f(0,1).

Now you are in trouble:

?- f(0,1).    % f(0,1) is in the truth set
true.

?- f(0,_).    % there is no f/2 in the truth set with 0 on first position!
false.

?- f(_,1).    % there is no f/2 in the truth set with 1 on second position!
false.

Failure-Slice Debugging Technique

From the Stack Overflow tag for failure-slice

A failure-slice is a fragment of a Prolog program obtained by inserting one or more false goals somewhere in it. Failure-slices help to localize reasons for universal non-termination of a pure monotonic Prolog program. They also help to give a lower bound for the number of inferences needed. It is a concrete program-slicing technique.

References

Localizing and explaining reasons for non-terminating logic programs with failure-slices (Ulrich Neumerkel, Fred Mesnard, September 1999)

See also

• Questions tagged [failure-slice])
• Example: Fibonacci Series Infinite Loop