Equation Icon  5 ( )P (k )P (k )f (k ) + 2perm. fNL,𝜃 = --cos ⃗k1 ∧ ⃗k2--0--1--0--2--s-3----------- , (4.5.8 ) 3 P0(k1)P0 (k2) + 2perm.