re root.
  var sqrt = motor => ((Math.sign(motor.s) + motor)*(1 + 0.5*(motor.s + motor.Grade(4)))).Normalized;

  // motors can be interpolated (similar to quaternions in two ways).
  var lerp = (motor, x) => (Math.sign(motor().s)*(1-x) + x*motor).Normalized;

  // Create some points (P), lines (l), planes (p) to illustrate.
  var P1 = point(0,0,-1),       P2 = point(.3,0.4,-1),
      p1 = plane(0,1,0,0.2),    p2 = plane(-0.5,0.5,0,.5),
      l1 = line(0,0,.5,.1,1,0), l2 = line(0,0,.7,-.1,1,0);
      
  // 