Lean4
/-- Equivalent categories have equivalent joins. -/
@[simps]
def mapPairEquiv (e : C ≌ C') (e' : D ≌ D') : C ⋆ D ≌ C' ⋆ D'
where
functor := mapPair e.functor e'.functor
inverse := mapPair e.inverse e'.inverse
unitIso := mapPairId.symm ≪≫ mapIsoWhiskerRight e.unitIso _ ≪≫ mapIsoWhiskerLeft _ e'.unitIso ≪≫ mapPairComp _ _ _ _
counitIso :=
(mapPairComp _ _ _ _).symm ≪≫ mapIsoWhiskerRight e.counitIso _ ≪≫ mapIsoWhiskerLeft _ e'.counitIso ≪≫ mapPairId
functor_unitIso_comp x := by cases x <;> simp [← (inclLeft C' D').map_comp, ← (inclRight C' D').map_comp]