Philatelic literature is divided into the following categories: Stamp catalogs, Periodicals, Auction catalogs, Books, Bibliographies, and Background Material.
∀x (PhilatelicLit(x) → (Stamp(x) ∨ Periodical(x) ∨ Auction(x) ∨ Book(x) ∨ Bibliography(x) ∨ Background(x)))