reserve q,r,c,c1,c2,c3 for Quaternion;
reserve x1,x2,x3,x4,y1,y2,y3,y4 for Real;

theorem Th10:
  r <> 0 implies |.r.| > 0
proof
  assume r <> 0;
  then |.r.| <> 0 by Lm4;
  hence thesis by QUATERNI:67;
end;
