A subdomain Omega contained in a domain A in the Riemann sphere is cal
led a relative circle domain in A if each component of A - Omega is ei
ther a closed disk or a point. Let Omega be a relative circle domain i
n the unit disk U in the complex plane C; and let A be a simply connec
ted proper subdomain of C. Then Omega is conformally homeomorphic to a
relative circle domain in A.