reserve U0,U1,U2,U3 for Universal_Algebra,
  n for Nat,
  x,y for set;
reserve A for non empty Subset of U0,
  o for operation of U0,
  x1,y1 for FinSequence of A;

theorem
  for U0 be with_const_op Universal_Algebra, U1 be SubAlgebra of U0
  holds Constants(U0) is non empty Subset of U1 by Th15;
