.PS
cct_init

# Usual defs...
qrt=dimen_/4;
hlf=dimen_/2;
dim=dimen_;

C1:circle radius 2*dim fill 0.9
# Order of painting is important! C2 before all other lines... 
C2:circle radius 1.5*dim fill 1 dashed at C1.center
line -> from C1.center to C1.nw
"$a$" at last line.center +(0.2*dim,0.2*dim) ljust_
line <-> from C2.e to C1.e
"$\delta$" at last line.center above_
"$\delta\ll a$" at C1.ne above_ ljust_

"\tiny Skin" at (2.5*dim,-2.5*dim)
.PE