Set: pp::colors
  Set: pp::unicode
  Set: lean::pp::implicit
  Defined: TypeM
  Assumed: g
  Assumed: B
  Assumed: B'
  Assumed: H
g B
===>
g B'
@congr2 TypeM TypeM B B' g (@to_eq TypeM B B' (@to_heq Type B B' H))
@eq TypeM (g B) (g B')