theorem Th64:
  i in Seg width G & width G > 0 implies width G = width DelCol(G,i) + 1
proof
  assume that
A1: i in Seg width G and
A2: width G > 0;
  ex m st width G = m+1 by A2,NAT_1:6;
  hence thesis by A1,Th63;
end;
