theorem Th76:
  Col(<*pf*>@,1) = pf
  proof
    len <*pf*> = 1 by FINSEQ_1:39;
    then
    dom <*pf*> = Seg 1 by FINSEQ_1:def 3;
    then Col(<*pf*>@,1) = Line(<*pf*>,1) by FINSEQ_1:1,MATRIX_0:58;
    hence thesis by Th72;
  end;
