||Iterator for iterating over all of the molecules in a globalized graph.
||Reperesnts a facotry for creating non-empty iterators over
a globalized graph.
||Iterator over molecules in a globalized graph, where one of the nodes in a triple is fixed.
||Represents an globalized graph iterator where all three nodes are
fixes (i.e. no wildcards).
||Globalized Graph iterator where 2 nodes are fixed.