bool less_than(bam1_t *a, bam1_t *b) {
int32_t ap1 = min(a->core.pos, a->core.mpos);
int32_t ap2 = max(a->core.pos, a->core.mpos);
int32_t bp1 = min(b->core.pos, b->core.mpos);
int32_t bp2 = max(b->core.pos, b->core.mpos);
bool less_than(bam1_t *a, bam1_t *b) {
int32_t ap1 = min(a->core.pos, a->core.mpos);
int32_t ap2 = max(a->core.pos, a->core.mpos);
int32_t bp1 = min(b->core.pos, b->core.mpos);
int32_t bp2 = max(b->core.pos, b->core.mpos);