theorem Th2:
  0.(K,n) is Idempotent Nilpotent
proof
  width 0.(K,n,n)=n & len 0.(K,n,n)=n by MATRIX_0:24;
  then 0.(K,n,n)*(0.(K,n))=0.(K,n,n) by MATRIX_6:1;
  hence thesis;
end;
