theorem Th23:
  u "/\" pseudo_compl(A).u = Bottom NormForm A
proof
  reconsider zero = {} as Element of Normal_forms_on A by NORMFORM:31;
A1: @(pseudo_compl(A).u) = mi(-@u) by Def8;
  thus u "/\" pseudo_compl(A).u = M(A).(u, pseudo_compl(A).u) by LATTICES:def 2
    .= mi(@u ^ mi(-@u)) by A1,NORMFORM:def 12
    .= mi(@u ^ -@u) by NORMFORM:51
    .= mi(zero) by Th21
    .= {} by NORMFORM:40,XBOOLE_1:3
    .= Bottom NormForm A by NORMFORM:57;
end;
