theorem
  <i> * <i> = -1
proof
  <i> = [*zz,jj,zz,zz*] by Lm2,Lm3; then
A1: <i> * <i> = [* 0*0-1*1-0*0-0*0, 0*1+1*0+0*0-0*0,
  0*0+0*0+1*0-0*1, 0*0+0*0+1*0-0*1 *] by Def9
    .= [*-1,0,0,0*];
  -1 = [*-jj,zz*] by ARYTM_0:def 5;
  hence thesis by A1,Lm3;
end;
