theorem
  width G = m+1 & m>0 & k in Seg m & n in dom G implies DelCol(G,1)*(n,k
  ) = G*(n,k+1) & 1 in Seg width G
proof
  assume that
A1: width G = m+1 and
A2: m>0 and
A3: k in Seg m and
A4: n in dom G;
  1<=width G by A1,A2,SEQM_3:43;
  then
A5: 1 in Seg width G by FINSEQ_1:1;
  1<=k & k<=m by A3,FINSEQ_1:1;
  hence thesis by A1,A4,A5,Th70;
end;
