L0:y=x+1
x=1,y=2
L2(x,y)
xL2+xL1=2xL0,yL2+yL1=2yL0
x+xL1=2*1=2
xL1=2-x
yL1=2*2-y=4-y
L1:yL1=2xL1-1
4-y=2*(2-x)-1
L2:2x-y+2=0