Lean4
/-- Homotopy equivalence is a transitive relation. -/
@[trans]
def trans {C D E : HomologicalComplex V c} (f : HomotopyEquiv C D) (g : HomotopyEquiv D E) : HomotopyEquiv C E
where
hom := f.hom ≫ g.hom
inv := g.inv ≫ f.inv
homotopyHomInvId := by simpa using ((g.homotopyHomInvId.compRightId f.inv).compLeft f.hom).trans f.homotopyHomInvId
homotopyInvHomId := by simpa using ((f.homotopyInvHomId.compRightId g.hom).compLeft g.inv).trans g.homotopyInvHomId