code: public static Vector3D_F64 constraint(TrifocalTensor tensor,
  										  Vector3D_F64 l1, Vector3D_F64 l2, Vector3D_F64 l3,
  										  @Nullable Vector3D_F64 ret)
  	{
  		if( ret == null )
  			ret = new Vector3D_F64();
  
  		double x = GeometryMath_F64.innerProd(l2, tensor.T1, l3);
  		double y = GeometryMath_F64.innerProd(l2, tensor.T2, l3);
  		double z = GeometryMath_F64.innerProd(l2, tensor.T3, l3);
  
  		GeometryMath_F64.cross(new Vector3D_F64(x, y, z), l1, ret);
  
  		return ret;
  	}
docs: <p>
  Trifocal tensor with line-line-line correspondence:<br>
  (l2<sup>T</sup>*[T1,T2,T3]*L2)*[l1]<sub>x</sub> = 0
  </p>
  
  @param tensor Trifocal tensor
  @param l1 A line in the first view.
  @param l2 A line in the second view.
  @param l3 A line in the third view.
  @param ret Storage for output.  If null a new instance will be declared.
  @return Result of applying the constraint.  With perfect inputs will be zero.