Definition mkinitial_SM (mu: SM_Injection) frgnS frgnT :=
  match mu with
  Build_SM_Injection locBSrc locBTgt pSrc pTgt local extBSrc extBTgt fSrc fTgt extern =>
  Build_SM_Injection (fun b => false) (fun b => false) (fun b => false) (fun b => false) (fun b => None)
                     (DomSrc mu) (DomTgt mu) frgnS frgnT (as_inj mu)
  end.

Lemma mkinitial_SM_extern: forall mu S T, extern_of (mkinitial_SM mu S T) = as_inj mu.