.PS
circlerad=0.1
ellipseht = 0.2
A: circle "$C_1$"
B: circle "$C_2$" at A + (0.5,0)
C: ellipse invis "$\ldots$" at B + (0.5,0)
D: circle "$C_n$" at C + (0.5,0)
E: circle "$I_1$" at A - (0,0.5)
F: circle "$I_2$" at B - (0,0.5)
G: ellipse invis "$\ldots$" at C - (0,0.5)
H: circle "$I_n$" at D - (0,0.5)
J: circle "$E$" at 1/2 - (0,0.5)
K: circle invis "$f$" at J + (0.3,0.04)
arrow from A.b to E.t
arrow from B.b to F.t
arrow from D.b to H.t
arrow from E to J chop
arrow from F to J chop
arrow from H to J chop
.PE