C U T S
A cut prunes or “cuts out” an unexplored part of a Prolog search tree.
Cuts can make a computation more efficient by eliminating futile search and backtracking.
Cuts are controversial because they are impure.
A cut is written as “ ! ” .
B : - C1 , ... , Cj-1 , ! , Cj+1 , ... , Ck
is applied, the cut tells control to backtrack past
Cj-1 , . . . , C1 , and B without considering any more rules for them.