Schematic representation of the variation of the energy gap (order parameter) plotted as function of the local angle circling the hole () and electron () Fermi surfaces of the material. Dashed line represents . (a) Isotropic state. (b) Anisotropic state with nodes on pockets. (c) Same as (b) but for a state with marginal (“kissing”) nodes. (d) Same as (b) but for deep gap minima.