Negated predicates

If a predicate is preceeded by a NOT, it is negated. Then the generated code tests that no edge between the two variables of the predicate exists, and skips all combinations of nodes which are linked by a corresponding edge. Negation is allowed in the following contexts:

• In rule tests if predicates are used that are graph functor instantiations. Negation can only be performed if a universe is known against the completion of a set of nodes is performed. This is the case only for graph functors, in which the set of graph nodes represents this universe. Negation is performed by a loop over the universe, skipping those nodes which are the neighbor set of the predicate.
• In rule tests for bitset predicates. They also have a universe which consists of all nodes the bits refer to. Negation is performed by a bitset complement.

• In rule transformations. Then in the code an edge of the denoted graph is deleted, not added.