u1, u2, x1, x2, x3, x4, 
(x1-u1)*(x1-1)+(x2-u2)*x2
(x1-1)^2+x2^2-1
u1*x4-u2*x3
x4*(x1-2)-x2*(x3-2)
(u1-x1)^2+(u2-x2)^2-(u1-x3)^2-(u2-x4)^2
