if (snapshot_compare(pair_test, new_pair) == 0) {
XBT_INFO("Pair %d already reached (equal to pair %d) !", new_pair->num, pair_test->num);
xbt_fifo_shift(mc_stack);
if (snapshot_compare(pair_test, new_pair) == 0) {
XBT_INFO("Pair %d already reached (equal to pair %d) !", new_pair->num, pair_test->num);
xbt_fifo_shift(mc_stack);