reserve k,n,m,l,p for Nat;
reserve n0,m0 for non zero Nat;
reserve f for FinSequence;
reserve x,X,Y for set;

theorem Th6:
  f is one-to-one implies Del(f,n) is one-to-one
proof
  Sgm (dom f \ {n}) is one-to-one by FINSEQ_3:92;
  hence thesis;
end;
