  We consider the problem of private information retrieval (PIR) where a single
user with private side information aims to retrieve multiple files from a
library stored (uncoded) at a number of servers. We assume the side information
at the user includes a subset of files stored privately (i.e., the server does
not know the indices of these files). In addition, we require that the identity
of the requests and side information at the user are not revealed to any of the
servers. The problem involves finding the minimum load to be transmitted from
the servers to the user such that the requested files can be decoded with the
help of received and side information. By providing matching lower and upper
bounds, for certain regimes, we characterize the minimum load imposed to all
the servers (i.e., the capacity of this PIR problem). Our result shows that the
capacity is the same as the capacity of a multi-message PIR problem without
private side information, but with a library of reduced size. The effective
size of the library is equal to the original library size minus the size of
side information.
