Set: pp::colors
  Set: pp::unicode
  Imported 'heq'
  Set: lean::pp::implicit
  Assumed: g
  Assumed: B
  Assumed: B'
  Assumed: H
g B
===>
g B'
@congr2 TypeM TypeM B B' g (@subst Type B B' (λ x : Type, @eq TypeM B x) (@refl TypeM B) H)
@eq TypeM (g B) (g B')