==>
Graph replacement rule, where one sub-graph (often only one object) is replaced by another graph. The connections between the host graph and the newly-inserted graph are recovered. That means that if, e.g., in a one-dimensional graph [ A B C D ] the node B is replaced by a node G, then G will be inserted into the graph with the original connecting edges to the neighbourhood of the node B: [ A G C D ]. The blank space indicates here a successor edge in XL. Axiom ==> A B C D; B ==> G;
Note: This is a from the module instantiation declarations (which also use the symbol ==>).