An artist’s rendering of the hole () and electron () pockets on a -pnictide Fermi surface (FS). With moderately sized and found by Yang et al.  the main dynamical feature of pnictides is the nesting tendency between these pockets at wave vector . The particle-hole interband repulsion induces SDW while its particle-particle counterpart favors a interband superconductor. Such superconductor comes in two varieties: in the type-A case both and pockets are superconducting on their own, with providing an additional boost. The intrinsic type-B interband superconductivity is entirely due to and has only a single order parameter , in contrast to the type-A.