theorem Th21:
  r*<e1> = |[ r,0,0 ]|
proof
<e1>.1 = 1 & <e1>.2 = 0 & <e1>.3 = 0;
    then r*<e1> = |[ r*1,r*0,r*0 ]| by Lm1  .= |[ r,0,0 ]|;
   hence thesis;
end;
