theorem Th2:
  [1,1] in [:Seg 3,Seg 1:] & [2,1] in [:Seg 3,Seg 1:] &
  [3,1] in [:Seg 3,Seg 1:]
  proof
    1 in Seg 3 & 2 in Seg 3 & 3 in Seg 3 & 1 in Seg 1 by FINSEQ_1:1;
    hence thesis by ZFMISC_1:87;
  end;
