theorem SquaredCarrier:
  the carrier of (B squared-latt) = B squared
  proof
    set L = [:B,B:];
    set P = B squared;
    consider o1,o2 being BinOp of P such that
A1: o1 = (the L_join of L)||P & o2 = (the L_meet of L)||P &
    latt ([:B,B:], P) = LattStr (#P, o1, o2#) by FILTER_2:def 14;
    thus thesis by A1;
  end;
