We use induction on n. Taking into account the initial conditions
(2), we note that the equation (5) is valid for n = 0 and n = 1. Now assume
that (5) is true for 0 ≤ s ≤ n, that is, jk,s = rs
1 + rs
2, for every s ∈{0,... ,n}.
Using (1) and taking in account that r1r2 = −2 we have