
theorem
  for S be locally_directed OrderSortedSign, U1 be non-empty OSAlgebra
of S, E be MSEquivalence-like (OrderSortedRelation of U1), s1,s2 be Element of
S, x be Element of (the Sorts of U1).s1 st s1 <= s2 holds for y being Element
  of (the Sorts of U1).s2 st y = x holds OSClass(E,x) = OSClass(E,y) by Th4;
