CPSC 3520 - DAY 8
FEBRUARY 6, 2018

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! will erase all other backtracking points.

Not 
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not(P) :- call (P), !, fail.
not (P).

Observe how the use of call, the cut (!), fail and Prologl's backtracking
mechanism (note order) allow implementation of the not predicate.

Cell Products
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["A","B"] ["C","D"]

["AC","AD","BC","BD"]