diff --git a/bwamem.c b/bwamem.c
index 52c4a18..2a35fe7 100644
--- a/bwamem.c
+++ b/bwamem.c
@@ -81,7 +81,7 @@ static int test_and_merge(const memopt_t *opt, memchain1_t *c, const memseed_t *
 	return 0;
 }
 
-void mem_insert_seed(const memopt_t *opt, kbtree_t(chn) *tree, smem_i *itr)
+static void mem_insert_seed(const memopt_t *opt, kbtree_t(chn) *tree, smem_i *itr)
 {
 	while (smem_next(itr) > 0) {
 		int i;
@@ -89,21 +89,22 @@ void mem_insert_seed(const memopt_t *opt, kbtree_t(chn) *tree, smem_i *itr)
 			bwtintv_t *p = &itr->matches->a[i];
 			int slen = (uint32_t)p->info - (p->info>>32); // seed length
 			int64_t k;
-			if (slen >= opt->min_seed_len || p->x[2] > opt->max_occ) continue;
+			if (slen < opt->min_seed_len || p->x[2] > opt->max_occ) continue;
 			for (k = 0; k < p->x[2]; ++k) {
 				memchain1_t tmp, *lower, *upper;
-				memseed_t c1;
+				memseed_t s;
 				int to_add = 0;
-				c1.rbeg = tmp.pos = bwt_sa(itr->bwt, p->x[0] + k);
-				c1.qbeg = p->info>>32;
-				c1.len  = slen;
+				s.rbeg = tmp.pos = bwt_sa(itr->bwt, p->x[0] + k);
+				s.qbeg = p->info>>32;
+				s.len  = slen;
 				if (kb_size(tree)) {
 					kb_intervalp(chn, tree, &tmp, &lower, &upper);
-					if (!test_and_merge(opt, lower, &c1)) to_add = 1;
-				} to_add = 1;
+					if (!lower || !test_and_merge(opt, lower, &s)) to_add = 1;
+				} else to_add = 1;
 				if (to_add) {
 					tmp.n = 1; tmp.m = 4;
 					tmp.seeds = calloc(tmp.m, sizeof(memseed_t));
+					tmp.seeds[0] = s;
 					kb_putp(chn, tree, &tmp);
 				}
 			}
@@ -111,7 +112,7 @@ void mem_insert_seed(const memopt_t *opt, kbtree_t(chn) *tree, smem_i *itr)
 	}
 }
 
-memchain_t mem_collect_seed(const memopt_t *opt, const bwt_t *bwt, int len, const uint8_t *seq)
+memchain_t mem_chain(const memopt_t *opt, const bwt_t *bwt, int len, const uint8_t *seq)
 {
 	memchain_t chain;
 	smem_i *itr;
@@ -122,6 +123,14 @@ memchain_t mem_collect_seed(const memopt_t *opt, const bwt_t *bwt, int len, cons
 	tree = kb_init(chn, KB_DEFAULT_SIZE);
 	itr = smem_itr_init(bwt);
 	smem_set_query(itr, 1, len, seq);
+	mem_insert_seed(opt, tree, itr);
+
+	chain.m = kb_size(tree); chain.n = 0;
+	chain.chains = malloc(chain.m * sizeof(memchain1_t));
+
+	#define traverse_func(p_) (chain.chains[chain.n++] = *(p_))
+	__kb_traverse(memchain1_t, tree, traverse_func);
+	#undef traverse_func
 
 	smem_itr_destroy(itr);
 	kb_destroy(chn, tree);
diff --git a/bwamem.h b/bwamem.h
index cc86ef2..72d9557 100644
--- a/bwamem.h
+++ b/bwamem.h
@@ -11,7 +11,8 @@ typedef struct {
 } smem_i;
 
 typedef struct {
-	int64_t qbeg, rbeg, len;
+	int64_t rbeg;
+	int32_t qbeg, len;
 } memseed_t;
 
 typedef struct {
@@ -41,6 +42,8 @@ int smem_next(smem_i *itr);
 
 memopt_t *mem_opt_init(void);
 
+memchain_t mem_chain(const memopt_t *opt, const bwt_t *bwt, int len, const uint8_t *seq);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/fastmap.c b/fastmap.c
index 6a41aeb..85ccd5c 100644
--- a/fastmap.c
+++ b/fastmap.c
@@ -16,7 +16,9 @@ int main_mem(int argc, char *argv[])
 	memopt_t *opt;
 	bwt_t *bwt;
 	bntseq_t *bns;
-	int c;
+	int i, j, c;
+	gzFile *fp;
+	kseq_t *seq;
 
 	opt = mem_opt_init();
 	while ((c = getopt(argc, argv, "")) >= 0) {
@@ -28,6 +30,38 @@ int main_mem(int argc, char *argv[])
 		free(opt);
 		return 1;
 	}
+	fp = gzopen(argv[optind + 1], "r");
+	seq = kseq_init(fp);
+	{ // load the packed sequences, BWT and SA
+		char *tmp = calloc(strlen(argv[optind]) + 5, 1);
+		strcat(strcpy(tmp, argv[optind]), ".bwt");
+		bwt = bwt_restore_bwt(tmp);
+		strcat(strcpy(tmp, argv[optind]), ".sa");
+		bwt_restore_sa(tmp, bwt);
+		free(tmp);
+		bns = bns_restore(argv[optind]);
+	}
+	while (kseq_read(seq) >= 0) {
+		memchain_t chain;
+		printf(">%s\n", seq->name.s);
+		for (i = 0; i < seq->seq.l; ++i)
+			seq->seq.s[i] = nst_nt4_table[(int)seq->seq.s[i]];
+		chain = mem_chain(opt, bwt, seq->seq.l, (uint8_t*)seq->seq.s);
+		for (i = 0; i < chain.n; ++i) {
+			memchain1_t *p = &chain.chains[i];
+			printf("%d\t%d", i, p->n);
+			for (j = 0; j < p->n; ++j) {
+				bwtint_t pos;
+				int is_rev, ref_id;
+				pos = bns_depos(bns, p->seeds[j].rbeg, &is_rev);
+				if (is_rev) pos -= p->seeds[j].len - 1;
+				bns_cnt_ambi(bns, pos, p->seeds[j].len, &ref_id);
+				printf("\t%d,%d,%s:%c%ld", p->seeds[j].len, p->seeds[j].qbeg, bns->anns[ref_id].name, "+-"[is_rev], (long)(pos - bns->anns[ref_id].offset) + 1);
+			}
+			putchar('\n');
+		}
+		puts("//");
+	}
 
 	free(opt);
 	return 0;