Let L be a list of positive integers (x₁, x₂, … x_n), and define

 t = Σ(L)

be the sum of all numbers in list L.

The following function f is a reduction from PP to SSP.

1. If t is odd, then f (L) = ((2), 1). That is, it is a SSP input whose answer is no.

2. If t is even, then f (L) = (L, t/2).

It should be clear that L ∈ PP if and only if f (L) ∈ SSP.