nes (i.e. coreference links, lines of identity,
    ligatures) in various graph notations.

 3. Locally defined names, AKA variables, which were first
    introduced by Aristotle and popularized by Euclid.  They
    were never called "variables" until they were used to
    represent physical quantities in the 17th century, and in
    logic, it is incorrect to call them variables, since they
    don't actually "vary".

Bottom line:  variables don't exist except in certain kinds
of languages.  They would be d