Prove that, for any structure function , (x) = xi(1i , x)+(1 xi)(0i , x) where (1i

Prove that, for any structure function φ,

φ(x) = xiφ(1i , x)+(1 −xi)φ(0i , x)
where (1i , x) = (x1, . . . , xi−1, 1, xi+1, . . . , xn), (0i , x) = (x1, . . . , xi−1, 0, xi+1, . . . , xn)