The reusable names table was being emptied as identifiers were used. This was sub-optimal for function parameters, because new identifiers would need to be created when exhausted.
Reset the reusable names list to a saved copy every time a new parameter list is started, in a similar fashion to what we did with the sequentially generated identifiers.
Rather than using tuples for set belonging, use a frozen set. That eliminates the need to separate them by lengths.
Also, 'Pop' is not a reserved word. It's perfectly valid as a possible substitution identifier, so allow it. If used, it will go to the used words anyway and thus will be skipped by the sequential name generator.
Identifiers can be equal if they belong to different syntactic scopes. That will allow better reuse and less creation of new identifiers, most notably as function and event parameter names.
The implementation would require a stack of counters where the current value is pushed when entering a new scope, and popped when exiting, rather than using a single counter for the whole program.
