A variable with name label
.
When the body
Formula succeeds, atoms in head
are true.
Disjunction (or) of the list of clauses.
A formula consists of variables, negation, and conjunction (and).
A literal is an Atom or its negation|Negated.
A negated atom, in the sense of negation as failure, not logical negation.
A negated atom, in the sense of negation as failure, not logical negation.
That is, it is true if atom
is not known/defined.
A formula consists of variables, negation, and conjunction (and). (Disjunction is not currently included- it is modeled at the level of a sequence of clauses. This is less convenient when defining clauses, but is not less powerful.)