
theorem Th16:
  for L being non empty RelStr, x being object holds x is Element of
  ClosureSystems L iff x is strict closure System of L
proof
  let L be non empty RelStr, x be object;
  x is Element of ClosureSystems L implies x is Element of Sub L by YELLOW_0:58
;
  then x is Element of ClosureSystems L implies x is strict SubRelStr of L by
Def2;
  hence thesis by Def3;
end;
