Question 19
two circles $\gamma_{1}$ and $\gamma_{2}$ of $A$ and $B$ centers are given in the plane, and intersecting in two points $C$ and $D$. Assume that the through circumference for $A$, $B$ and $C$ intersects further $\gamma_{1}$ and $\gamma_{2}$ in $E$ and $F$ respectively, and that the arc $E F$ not containing $C$ lie out of the two circles delimited by $\gamma_{1}$ and $\gamma_{2}$. Prove that the $E F$ arc not containing $C$ is bisected by the line $C D$.