add unicode notation for identity_modality
simpl rewrite
Use -2 and -1 rather than minus_two and minus_one
Merge pull request #511 from JasonGross/neg-trunc-notation

Use -2 and -1 rather than minus_two and minus_one
Merge pull request #507 from mikeshulman/rsu-without-funext

Merging as per @mikeshulman 's suggestion.

eliminate funext (mostly) from reflective subuniverses
WIP

WIP

WIP

Fill in proof from @mikeshulman