Production Ambiguity

[drobertadams]

There is no way to distinguish new from old vertices on the RHS. For example, the production A ==> A -> A either means (1) insert a new A before the existing A, or (2) insert a new A after the existing A. It's ambiguous. One solution would be to use label numbers: A1 ==> A1 -> A2.

Question: Do new RHS vertices require numbers? E.g., A1 ==> A1 -> A, or how about A1 ==> A1 -> A2, or allow both.