Why does new_op and new_var take optional args

[WalterSmuts]

I'm trying to find the explanation for the question in the title and it seems unnecessary. What situation whould you pass none?

Consider adding the answer in the docs too.

[joshrule]

Good question - having a name is useful when you are a human directly interacting with a term rewriting system (TRS) and want human-memorable names for things. When interacting with a TRS programmatically, however, human-memorable names are relatively unimportant, because nearly all of the interaction with the TRS will be done by the machine rather than by a human. In that case, it's much easier not to have a name beyond the variable/operator ID.

I'm happy to add something to that effect to the docs if you submit a PR.