prologue_return ret = prologue(n);
for (int j = 0; j != 100; ++j) {
size_t offset = rnd_engine() % ret.size;
size_t size = rnd_engine() % (ret.size - offset);
prologue_return ret = prologue(n);
for (int j = 0; j != 100; ++j) {
size_t offset = rnd_engine() % ret.size;
size_t size = rnd_engine() % (ret.size - offset);