theorem Th66:
  i in Seg width G & width G > 1 & n in dom G & m in Seg width
  DelCol(G,i) implies DelCol(G,i)*(n,m)=Del(Line(G,n),i).m
proof
  assume that
A1: i in Seg width G & width G > 1 & n in dom G and
A2: m in Seg width (DelCol(G,i));
  thus DelCol(G,i)*(n,m) = Line(DelCol(G,i),n).m by A2,Def7
    .= Del(Line(G,n),i).m by A1,Th62;
end;
