theorem Th79:
  Top latt (L,(.p.>) = p
proof
  latt (L,(.p.>) = (latt (L.:,(.p.>.:)).: by Th70
    .= (latt (L.:,<.p.:.))).: by Th29
    .= (latt <.p.:.)).: by Th69;
  hence Top latt (L,(.p.>) = Bottom latt <.p.:.) by LATTICE2:61
    .= p by FILTER_0:56;
end;
