`:#` instead of `$#`?

[gilch]

Gensyms are a reader-level Lissp concept, so how the EDN Hissps feel about this is irrelevant. It seems closer to the Common Lisp meaning of #:. That would free up $# for (alias $ unittest.mock..sentinel). (Mnemonic is $entinel.) Or maybe :# should be the sentinels and gensyms can stay. Sentinels kind of feel like Lisp keywords because they're interned, and : says "keyword" in Lisp (even though #: kind of doesn't).