Lean4
/-- A pointfree version of `colimitIso`, stating that whiskering by `F` followed by taking the
colimit is isomorpic to taking the colimit on the codomain of `F`. -/
def colimIso [HasColimitsOfShape D E] [HasColimitsOfShape C E] :
(whiskeringLeft _ _ _).obj F ⋙ colim ≅ colim (J := D) (C := E) :=
NatIso.ofComponents (fun G => colimitIso F G) fun f =>
by
simp only [comp_obj, whiskeringLeft_obj_obj, colim_obj, comp_map, whiskeringLeft_obj_map, colim_map, colimitIso_hom]
ext
simp only [comp_obj, ι_colimMap_assoc, whiskerLeft_app, colimit.ι_pre, colimit.ι_pre_assoc, ι_colimMap]