These are a pair of 4×4 matrices. They sum to the identity matrix: Λ Λ + ( p ) + Λ Λ − − ( p ) = I are orthogonal Λ Λ + ( p ) Λ Λ − − ( p ) = Λ Λ − − ( p ) Λ Λ + ( p ) = 0 and are idempotent Λ Λ ± ± ( p ) Λ Λ ± ± ( p ) = Λ Λ ± ± ( p )