  In the course of proving the strong perfect graph theorem, Chudnovsky,
Robertson, Seymour, and Thomas showed that every perfect graph either belongs
to one of five basic classes or admits one of several decompositions. Four of
the basic classes are closed under taking induced subgraphs (and have known
forbidden subgraph characterizations), while the fifth one, consisting of
double-split graphs, is not.
  A graph is doubled if it is an induced subgraph of a double-split graph. We
find the forbidden induced subgraph characterization of doubled graphs; it
contains 44 graphs.
