reserve a,x,y for object, A,B for set,
  l,m,n for Nat;
reserve X,Y for set, x for object,
  p,q for Function-yielding FinSequence,
  f,g,h for Function;

theorem Th44:
  compose(<*f*>,X) = f*id X
proof
  <*f*> = {}^<*f*> by FINSEQ_1:34;
  hence compose(<*f*>,X) = f*compose({},X) by Th40
    .= f*id X by Th38;
end;
