.PS
ellipse; ellipse with .nw at last ellipse.se
move up 1 right 1.5
circle "a"
circle "b" at 1st circle - (0.75,1)
circle "c" at 1st circle + (0.75,-1)
line from 1st circle to 2nd circle chop
line from 1st circle to 3rd circle chop
.PE
