
theorem Th21:
  for L being Boolean complemented lower-bounded upper-bounded
  distributive distributive' Lattice-like non empty LattStr holds Bottom L =
  Bot' L
proof
  let L be Boolean complemented lower-bounded upper-bounded distributive
  distributive' Lattice-like non empty LattStr;
  set Y = Bottom L;
  L is lower-bounded' & for a being Element of L holds Y "\/" a = a & a
  "\/" Y = a by Th15;
  hence thesis by Def4;
end;
