paste this code to here
u = 1cm;
pair a,b,o,c,d;
a := (0,2)*u;
b := (0,1)*u;
o := (0,0)*u;
c := (0,-1)*u;
d := (0,-2)*u;
fill a{right} .. o{left} .. d{right} .. {left}cycle;
draw a{left} .. d;
fill fullcircle scaled 6bp shifted b ;
path p;
p = fullcircle scaled 6bp shifted c;
fill p withcolor white;