Implement `iter_v`, `eval_i` and `eval_rho` for a binary prior, $P_0 (x) = \rho \delta(x) + (1 - \rho) \delta(x - 1)$.
Implement$P_0 (x) = \rho \delta(x) + (1 - \rho) \delta(x - 1)$ .
iter_v,eval_iandeval_rhofor a binary prior,