size(400); pair z0=(0,0); pair c0=(1,1); pair c1=(2,1); pair z1=(3,0); draw(z0..controls c0 and c1 .. z1,blue); draw(z0--c0--c1--z1,dashed); dot("$z_0$",z0,W,red); dot("$c_0$",c0,NW,red); dot("$c_1$",c1,NE,red); dot("$z_1$",z1,red);