Parton distributions in the photon from ${\gamma }^{\ast }\gamma$ and ${\gamma }^{\ast }p$ scattering

Leading order parton distributions in the photon are extracted from the existing $F_2^{\gamma }$ measurements and the low-$x$ proton structure function. The latter is related to the photon structure function by assuming Gribov factorization to hold at low $x$. The resulting parton distributions in the photon are found to be consistent with the Frankfurt-Gurvich sum rule for the photon.