inline rng_t operator^( const rng_t &r, const n_t &n ) { return rng_t( (r - n).first(), (r + n).last() ); }
inline rng_t ext(const rng_t &r, const n_t &n) { return rng_t( (r - n).first(), (r + n).last() ); }
slocuspop_popgenmut_custom_fixture(const unsigned seed = 0) : pop(poptype(1000)), rng(rng_t(seed)), generation(0) { }