reserve X for BCI-algebra;
reserve x,y,z,u,a,b for Element of X;
reserve IT for non empty Subset of X;

theorem Th33: ::tuilun1.3.3
  for a being Element of AtomSet(X),x being Element of X holds a\x
  in AtomSet(X)
proof
  let a be Element of AtomSet(X),x be Element of X;
  ((a\x)`)`=a\x by Th31;
  hence thesis by Th29;
end;
