reserve X,Y for set;
reserve R for domRing-like commutative Ring;
reserve c for Element of R;

theorem Th21:
  for R being well-unital non empty multLoopStr
  for X being Subset of R holds
    X in Classes R implies X is non empty
proof
  let R be well-unital non empty multLoopStr;
  let X be Subset of R;
  assume X in Classes R;
  then ex a being Element of R st X = Class a by Def6;
  hence thesis;
end;
