theorem SquaredTop:
  Top (B squared-latt) = [Top B, Top B]
  proof
    [Top B, Top B] in B squared; then
    Top [:B,B:] in B squared by FILTER_1:43; then
    Top latt ([:B,B:], B squared) = Top [:B,B:]  by ThC;
    hence thesis by FILTER_1:43;
  end;
