diff --git a/bwamem.c b/bwamem.c
index 0ecb190..65807fe 100644
--- a/bwamem.c
+++ b/bwamem.c
@@ -19,6 +19,15 @@ memopt_t *mem_opt_init()
  * SMEM iterator interface *
  ***************************/
 
+struct __smem_i {
+	const bwt_t *bwt;
+	const uint8_t *query;
+	int start, len;
+	bwtintv_v *matches; // matches; to be returned by smem_next()
+	bwtintv_v *sub;     // sub-matches inside the longest match; temporary
+	bwtintv_v *tmpvec[2]; // temporary arrays
+};
+
 smem_i *smem_itr_init(const bwt_t *bwt)
 {
 	smem_i *itr;
@@ -47,25 +56,25 @@ void smem_set_query(smem_i *itr, int len, const uint8_t *query)
 	itr->len = len;
 }
 
-int smem_next(smem_i *itr, int split_len)
+const bwtintv_v *smem_next(smem_i *itr, int split_len)
 {
 	int i, max, max_i;
-	itr->tmpvec[0]->n = itr->tmpvec[1]->n = itr->matches->n = 0;
-	if (itr->start >= itr->len || itr->start < 0) return -1;
+	itr->tmpvec[0]->n = itr->tmpvec[1]->n = itr->matches->n = itr->sub->n = 0;
+	if (itr->start >= itr->len || itr->start < 0) return 0;
 	while (itr->start < itr->len && itr->query[itr->start] > 3) ++itr->start; // skip ambiguous bases
-	if (itr->start == itr->len) return -1;
-	itr->start = bwt_smem1(itr->bwt, itr->len, itr->query, itr->start, 1, itr->matches, itr->tmpvec);
-	if (itr->matches->n == 0) return itr->start;
-	for (i = max = 0, max_i = 0; i < itr->matches->n; ++i) {
+	if (itr->start == itr->len) return 0;
+	itr->start = bwt_smem1(itr->bwt, itr->len, itr->query, itr->start, 1, itr->matches, itr->tmpvec); // search for SMEM
+	if (itr->matches->n == 0) return itr->matches; // well, in theory, we should never come here
+	for (i = max = 0, max_i = 0; i < itr->matches->n; ++i) { // look for the longest match
 		bwtintv_t *p = &itr->matches->a[i];
 		int len = (uint32_t)p->info - (p->info>>32);
 		if (max < len) max = len, max_i = i;
 	}
-	if (split_len > 0 && max >= split_len && itr->matches->a[max_i].x[2] == 1) {
+	if (split_len > 0 && max >= split_len && itr->matches->a[max_i].x[2] == 1) { // if the longest SMEM is unique and long
 		int j;
-		bwtintv_v *a = itr->tmpvec[0];
+		bwtintv_v *a = itr->tmpvec[0]; // reuse tmpvec[0] for merging
 		bwtintv_t *p = &itr->matches->a[max_i];
-		bwt_smem1(itr->bwt, itr->len, itr->query, ((uint32_t)p->info + (p->info>>32))>>1, 2, itr->sub, itr->tmpvec); // starting from the middle of the longest match
+		bwt_smem1(itr->bwt, itr->len, itr->query, ((uint32_t)p->info + (p->info>>32))>>1, 2, itr->sub, itr->tmpvec); // starting from the middle of the longest MEM
 		i = j = 0; a->n = 0;
 		while (i < itr->matches->n && j < itr->sub->n) { // ordered merge
 			if (itr->matches->a[i].info < itr->sub->a[j].info) {
@@ -80,7 +89,7 @@ int smem_next(smem_i *itr, int split_len)
 		for (; j < itr->sub->n; ++j)     kv_push(bwtintv_t, *a, itr->sub->a[j]);
 		kv_copy(bwtintv_t, *itr->matches, *a);
 	}
-	return itr->start;
+	return itr->matches;
 }
 
 #include "kbtree.h"
@@ -98,7 +107,7 @@ static int test_and_merge(const memopt_t *opt, memchain1_t *c, const memseed_t *
 		return 1; // contained seed; do nothing
 	x = p->qbeg - last->qbeg; // always positive
 	y = p->rbeg - last->rbeg;
-	if (y > 0 && x - y <= opt->w && y - x <= opt->w && x - last->len < opt->max_chain_gap && y - last->len < opt->max_chain_gap) {
+	if (y > 0 && x - y <= opt->w && y - x <= opt->w && x - last->len < opt->max_chain_gap && y - last->len < opt->max_chain_gap) { // grow the chain
 		if (c->n == c->m) {
 			c->m <<= 1;
 			c->seeds = realloc(c->seeds, c->m * sizeof(memseed_t));
@@ -106,30 +115,31 @@ static int test_and_merge(const memopt_t *opt, memchain1_t *c, const memseed_t *
 		c->seeds[c->n++] = *p;
 		return 1;
 	}
-	return 0;
+	return 0; // request to add a new chain
 }
 
 static void mem_insert_seed(const memopt_t *opt, kbtree_t(chn) *tree, smem_i *itr)
 {
-	while (smem_next(itr, opt->min_seed_len<<1) > 0) {
+	const bwtintv_v *a;
+	while ((a = smem_next(itr, opt->min_seed_len<<1)) != 0) { // to find all SMEM and some internal MEM
 		int i;
-		for (i = 0; i < itr->matches->n; ++i) {
-			bwtintv_t *p = &itr->matches->a[i];
+		for (i = 0; i < a->n; ++i) { // go through each SMEM/MEM up to itr->start
+			bwtintv_t *p = &a->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; // ignore if too short or too repetitive
 			for (k = 0; k < p->x[2]; ++k) {
 				memchain1_t tmp, *lower, *upper;
 				memseed_t s;
 				int to_add = 0;
-				s.rbeg = tmp.pos = bwt_sa(itr->bwt, p->x[0] + k);
+				s.rbeg = tmp.pos = bwt_sa(itr->bwt, p->x[0] + k); // this is the base coordinate in the forward-reverse reference
 				s.qbeg = p->info>>32;
 				s.len  = slen;
 				if (kb_size(tree)) {
-					kb_intervalp(chn, tree, &tmp, &lower, &upper);
+					kb_intervalp(chn, tree, &tmp, &lower, &upper); // find the closest chain
 					if (!lower || !test_and_merge(opt, lower, &s)) to_add = 1;
 				} else to_add = 1;
-				if (to_add) {
+				if (to_add) { // add the seed as a new chain
 					tmp.n = 1; tmp.m = 4;
 					tmp.seeds = calloc(tmp.m, sizeof(memseed_t));
 					tmp.seeds[0] = s;
diff --git a/bwamem.h b/bwamem.h
index 1ad9e77..eb79586 100644
--- a/bwamem.h
+++ b/bwamem.h
@@ -3,13 +3,8 @@
 
 #include "bwt.h"
 
-typedef struct {
-	const bwt_t *bwt;
-	const uint8_t *query;
-	int start, len;
-	bwtintv_v *matches; // matches
-	bwtintv_v *tmpvec[2], *sub; // these are temporary arrays
-} smem_i;
+struct __smem_i;
+typedef struct __smem_i smem_i;
 
 typedef struct {
 	int64_t rbeg;
@@ -39,7 +34,7 @@ extern "C" {
 smem_i *smem_itr_init(const bwt_t *bwt);
 void smem_itr_destroy(smem_i *itr);
 void smem_set_query(smem_i *itr, int len, const uint8_t *query);
-int smem_next(smem_i *itr, int split_len);
+const bwtintv_v *smem_next(smem_i *itr, int split_len);
 
 memopt_t *mem_opt_init(void);
 
diff --git a/fastmap.c b/fastmap.c
index 6e8a662..42122b4 100644
--- a/fastmap.c
+++ b/fastmap.c
@@ -76,6 +76,7 @@ int main_fastmap(int argc, char *argv[])
 	bwt_t *bwt;
 	bntseq_t *bns;
 	smem_i *itr;
+	const bwtintv_v *a;
 
 	while ((c = getopt(argc, argv, "w:l:ps")) >= 0) {
 		switch (c) {
@@ -111,9 +112,9 @@ int main_fastmap(int argc, char *argv[])
 		for (i = 0; i < seq->seq.l; ++i)
 			seq->seq.s[i] = nst_nt4_table[(int)seq->seq.s[i]];
 		smem_set_query(itr, seq->seq.l, (uint8_t*)seq->seq.s);
-		while (smem_next(itr, split_long? min_len<<1 : 0) > 0) {
-			for (i = 0; i < itr->matches->n; ++i) {
-				bwtintv_t *p = &itr->matches->a[i];
+		while ((a = smem_next(itr, split_long? min_len<<1 : 0)) != 0) {
+			for (i = 0; i < a->n; ++i) {
+				bwtintv_t *p = &a->a[i];
 				if ((uint32_t)p->info - (p->info>>32) < min_len) continue;
 				printf("EM\t%d\t%d\t%ld", (uint32_t)(p->info>>32), (uint32_t)p->info, (long)p->x[2]);
 				if (p->x[2] <= min_iwidth) {
diff --git a/kbtree.h b/kbtree.h
new file mode 100644
index 0000000..5ed5330
--- /dev/null
+++ b/kbtree.h
@@ -0,0 +1,384 @@
+/*-
+ * Copyright 1997-1999, 2001, John-Mark Gurney.
+ *           2008-2009, Attractive Chaos <attractor@live.co.uk>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef __AC_KBTREE_H
+#define __AC_KBTREE_H
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+
+typedef struct {
+	int32_t is_internal:1, n:31;
+} kbnode_t;
+
+#define	__KB_KEY(type, x)	((type*)((char*)x + 4))
+#define __KB_PTR(btr, x)	((kbnode_t**)((char*)x + btr->off_ptr))
+
+#define __KB_TREE_T(name)						\
+	typedef struct {							\
+		kbnode_t *root;							\
+		int	off_key, off_ptr, ilen, elen;		\
+		int	n, t;								\
+		int	n_keys, n_nodes;					\
+	} kbtree_##name##_t;
+
+#define __KB_INIT(name, key_t)											\
+	kbtree_##name##_t *kb_init_##name(int size)							\
+	{																	\
+		kbtree_##name##_t *b;											\
+		b = (kbtree_##name##_t*)calloc(1, sizeof(kbtree_##name##_t));	\
+		b->t = ((size - 4 - sizeof(void*)) / (sizeof(void*) + sizeof(key_t)) + 1) >> 1; \
+		if (b->t < 2) {													\
+			free(b); return 0;											\
+		}																\
+		b->n = 2 * b->t - 1;											\
+		b->off_ptr = 4 + b->n * sizeof(key_t);							\
+		b->ilen = (4 + sizeof(void*) + b->n * (sizeof(void*) + sizeof(key_t)) + 3) >> 2 << 2; \
+		b->elen = (b->off_ptr + 3) >> 2 << 2;							\
+		b->root = (kbnode_t*)calloc(1, b->ilen);						\
+		++b->n_nodes;													\
+		return b;														\
+	}
+
+#define __kb_destroy(b) do {											\
+		int i, max = 8;													\
+		kbnode_t *x, **top, **stack = 0;								\
+		if (b) {														\
+			top = stack = (kbnode_t**)calloc(max, sizeof(kbnode_t*));	\
+			*top++ = (b)->root;											\
+			while (top != stack) {										\
+				x = *--top;												\
+				if (x->is_internal == 0) { free(x); continue; }			\
+				for (i = 0; i <= x->n; ++i)								\
+					if (__KB_PTR(b, x)[i]) {							\
+						if (top - stack == max) {						\
+							max <<= 1;									\
+							stack = (kbnode_t**)realloc(stack, max * sizeof(kbnode_t*)); \
+							top = stack + (max>>1);						\
+						}												\
+						*top++ = __KB_PTR(b, x)[i];						\
+					}													\
+				free(x);												\
+			}															\
+		}																\
+		free(b); free(stack);											\
+	} while (0)
+
+#define __kb_get_first(key_t, b, ret) do {	\
+		kbnode_t *__x = (b)->root;			\
+		while (__KB_PTR(b, __x)[0] != 0)	\
+			__x = __KB_PTR(b, __x)[0];		\
+		(ret) = __KB_KEY(key_t, __x)[0];	\
+	} while (0)
+
+#define __KB_GET_AUX0(name, key_t, __cmp)								\
+	static inline int __kb_get_aux_##name(const kbnode_t * __restrict x, const key_t * __restrict k, int *r) \
+	{																	\
+		int tr, *rr, begin, end, n = x->n >> 1;							\
+		if (x->n == 0) return -1;										\
+		if (__cmp(*k, __KB_KEY(key_t, x)[n]) < 0) {						\
+			begin = 0; end = n;											\
+		} else { begin = n; end = x->n - 1; }							\
+		rr = r? r : &tr;												\
+		n = end;														\
+		while (n >= begin && (*rr = __cmp(*k, __KB_KEY(key_t, x)[n])) < 0) --n; \
+		return n;														\
+	}
+
+#define __KB_GET_AUX1(name, key_t, __cmp)								\
+	static inline int __kb_getp_aux_##name(const kbnode_t * __restrict x, const key_t * __restrict k, int *r) \
+	{																	\
+		int tr, *rr, begin = 0, end = x->n;								\
+		if (x->n == 0) return -1;										\
+		rr = r? r : &tr;												\
+		while (begin < end) {											\
+			int mid = (begin + end) >> 1;								\
+			if (__cmp(__KB_KEY(key_t, x)[mid], *k) < 0) begin = mid + 1; \
+			else end = mid;												\
+		}																\
+		if (begin == x->n) { *rr = 1; return x->n - 1; }				\
+		if ((*rr = __cmp(*k, __KB_KEY(key_t, x)[begin])) < 0) --begin;	\
+		return begin;													\
+	}
+
+#define __KB_GET(name, key_t)											\
+	static key_t *kb_getp_##name(kbtree_##name##_t *b, const key_t * __restrict k) \
+	{																	\
+		int i, r = 0;													\
+		kbnode_t *x = b->root;											\
+		while (x) {														\
+			i = __kb_getp_aux_##name(x, k, &r);							\
+			if (i >= 0 && r == 0) return &__KB_KEY(key_t, x)[i];		\
+			if (x->is_internal == 0) return 0;							\
+			x = __KB_PTR(b, x)[i + 1];									\
+		}																\
+		return 0;														\
+	}																	\
+	static inline key_t *kb_get_##name(kbtree_##name##_t *b, const key_t k) \
+	{																	\
+		return kb_getp_##name(b, &k);									\
+	}
+
+#define __KB_INTERVAL(name, key_t)										\
+	static void kb_intervalp_##name(kbtree_##name##_t *b, const key_t * __restrict k, key_t **lower, key_t **upper)	\
+	{																	\
+		int i, r = 0;													\
+		kbnode_t *x = b->root;											\
+		*lower = *upper = 0;											\
+		while (x) {														\
+			i = __kb_getp_aux_##name(x, k, &r);							\
+			if (i >= 0 && r == 0) {										\
+				*lower = *upper = &__KB_KEY(key_t, x)[i];				\
+				return;													\
+			}															\
+			if (i >= 0) *lower = &__KB_KEY(key_t, x)[i];				\
+			if (i < x->n - 1) *upper = &__KB_KEY(key_t, x)[i + 1];		\
+			if (x->is_internal == 0) return;							\
+			x = __KB_PTR(b, x)[i + 1];									\
+		}																\
+	}																	\
+	static inline void kb_interval_##name(kbtree_##name##_t *b, const key_t k, key_t **lower, key_t **upper) \
+	{																	\
+		kb_intervalp_##name(b, &k, lower, upper);						\
+	}
+
+#define __KB_PUT(name, key_t, __cmp)									\
+	/* x must be an internal node */									\
+	static void __kb_split_##name(kbtree_##name##_t *b, kbnode_t *x, int i, kbnode_t *y) \
+	{																	\
+		kbnode_t *z;													\
+		z = (kbnode_t*)calloc(1, y->is_internal? b->ilen : b->elen);	\
+		++b->n_nodes;													\
+		z->is_internal = y->is_internal;								\
+		z->n = b->t - 1;												\
+		memcpy(__KB_KEY(key_t, z), __KB_KEY(key_t, y) + b->t, sizeof(key_t) * (b->t - 1)); \
+		if (y->is_internal) memcpy(__KB_PTR(b, z), __KB_PTR(b, y) + b->t, sizeof(void*) * b->t); \
+		y->n = b->t - 1;												\
+		memmove(__KB_PTR(b, x) + i + 2, __KB_PTR(b, x) + i + 1, sizeof(void*) * (x->n - i)); \
+		__KB_PTR(b, x)[i + 1] = z;										\
+		memmove(__KB_KEY(key_t, x) + i + 1, __KB_KEY(key_t, x) + i, sizeof(key_t) * (x->n - i)); \
+		__KB_KEY(key_t, x)[i] = __KB_KEY(key_t, y)[b->t - 1];			\
+		++x->n;															\
+	}																	\
+	static void __kb_putp_aux_##name(kbtree_##name##_t *b, kbnode_t *x, const key_t * __restrict k) \
+	{																	\
+		int i = x->n - 1;												\
+		if (x->is_internal == 0) {										\
+			i = __kb_getp_aux_##name(x, k, 0);							\
+			if (i != x->n - 1)											\
+				memmove(__KB_KEY(key_t, x) + i + 2, __KB_KEY(key_t, x) + i + 1, (x->n - i - 1) * sizeof(key_t)); \
+			__KB_KEY(key_t, x)[i + 1] = *k;								\
+			++x->n;														\
+		} else {														\
+			i = __kb_getp_aux_##name(x, k, 0) + 1;						\
+			if (__KB_PTR(b, x)[i]->n == 2 * b->t - 1) {					\
+				__kb_split_##name(b, x, i, __KB_PTR(b, x)[i]);			\
+				if (__cmp(*k, __KB_KEY(key_t, x)[i]) > 0) ++i;			\
+			}															\
+			__kb_putp_aux_##name(b, __KB_PTR(b, x)[i], k);				\
+		}																\
+	}																	\
+	static void kb_putp_##name(kbtree_##name##_t *b, const key_t * __restrict k) \
+	{																	\
+		kbnode_t *r, *s;												\
+		++b->n_keys;													\
+		r = b->root;													\
+		if (r->n == 2 * b->t - 1) {										\
+			++b->n_nodes;												\
+			s = (kbnode_t*)calloc(1, b->ilen);							\
+			b->root = s; s->is_internal = 1; s->n = 0;					\
+			__KB_PTR(b, s)[0] = r;										\
+			__kb_split_##name(b, s, 0, r);								\
+			r = s;														\
+		}																\
+		__kb_putp_aux_##name(b, r, k);									\
+	}																	\
+	static inline void kb_put_##name(kbtree_##name##_t *b, const key_t k) \
+	{																	\
+		kb_putp_##name(b, &k);											\
+	}
+
+
+#define __KB_DEL(name, key_t)											\
+	static key_t __kb_delp_aux_##name(kbtree_##name##_t *b, kbnode_t *x, const key_t * __restrict k, int s) \
+	{																	\
+		int yn, zn, i, r = 0;											\
+		kbnode_t *xp, *y, *z;											\
+		key_t kp;														\
+		if (x == 0) return *k;											\
+		if (s) { /* s can only be 0, 1 or 2 */							\
+			r = x->is_internal == 0? 0 : s == 1? 1 : -1;				\
+			i = s == 1? x->n - 1 : -1;									\
+		} else i = __kb_getp_aux_##name(x, k, &r);						\
+		if (x->is_internal == 0) {										\
+			if (s == 2) ++i;											\
+			kp = __KB_KEY(key_t, x)[i];									\
+			memmove(__KB_KEY(key_t, x) + i, __KB_KEY(key_t, x) + i + 1, (x->n - i - 1) * sizeof(key_t)); \
+			--x->n;														\
+			return kp;													\
+		}																\
+		if (r == 0) {													\
+			if ((yn = __KB_PTR(b, x)[i]->n) >= b->t) {					\
+				xp = __KB_PTR(b, x)[i];									\
+				kp = __KB_KEY(key_t, x)[i];								\
+				__KB_KEY(key_t, x)[i] = __kb_delp_aux_##name(b, xp, 0, 1); \
+				return kp;												\
+			} else if ((zn = __KB_PTR(b, x)[i + 1]->n) >= b->t) {		\
+				xp = __KB_PTR(b, x)[i + 1];								\
+				kp = __KB_KEY(key_t, x)[i];								\
+				__KB_KEY(key_t, x)[i] = __kb_delp_aux_##name(b, xp, 0, 2); \
+				return kp;												\
+			} else if (yn == b->t - 1 && zn == b->t - 1) {				\
+				y = __KB_PTR(b, x)[i]; z = __KB_PTR(b, x)[i + 1];		\
+				__KB_KEY(key_t, y)[y->n++] = *k;						\
+				memmove(__KB_KEY(key_t, y) + y->n, __KB_KEY(key_t, z), z->n * sizeof(key_t)); \
+				if (y->is_internal) memmove(__KB_PTR(b, y) + y->n, __KB_PTR(b, z), (z->n + 1) * sizeof(void*)); \
+				y->n += z->n;											\
+				memmove(__KB_KEY(key_t, x) + i, __KB_KEY(key_t, x) + i + 1, (x->n - i - 1) * sizeof(key_t)); \
+				memmove(__KB_PTR(b, x) + i + 1, __KB_PTR(b, x) + i + 2, (x->n - i - 1) * sizeof(void*)); \
+				--x->n;													\
+				free(z);												\
+				return __kb_delp_aux_##name(b, y, k, s);				\
+			}															\
+		}																\
+		++i;															\
+		if ((xp = __KB_PTR(b, x)[i])->n == b->t - 1) {					\
+			if (i > 0 && (y = __KB_PTR(b, x)[i - 1])->n >= b->t) {		\
+				memmove(__KB_KEY(key_t, xp) + 1, __KB_KEY(key_t, xp), xp->n * sizeof(key_t)); \
+				if (xp->is_internal) memmove(__KB_PTR(b, xp) + 1, __KB_PTR(b, xp), (xp->n + 1) * sizeof(void*)); \
+				__KB_KEY(key_t, xp)[0] = __KB_KEY(key_t, x)[i - 1];		\
+				__KB_KEY(key_t, x)[i - 1] = __KB_KEY(key_t, y)[y->n - 1]; \
+				if (xp->is_internal) __KB_PTR(b, xp)[0] = __KB_PTR(b, y)[y->n]; \
+				--y->n; ++xp->n;										\
+			} else if (i < x->n && (y = __KB_PTR(b, x)[i + 1])->n >= b->t) { \
+				__KB_KEY(key_t, xp)[xp->n++] = __KB_KEY(key_t, x)[i];	\
+				__KB_KEY(key_t, x)[i] = __KB_KEY(key_t, y)[0];			\
+				if (xp->is_internal) __KB_PTR(b, xp)[xp->n] = __KB_PTR(b, y)[0]; \
+				--y->n;													\
+				memmove(__KB_KEY(key_t, y), __KB_KEY(key_t, y) + 1, y->n * sizeof(key_t)); \
+				if (y->is_internal) memmove(__KB_PTR(b, y), __KB_PTR(b, y) + 1, (y->n + 1) * sizeof(void*)); \
+			} else if (i > 0 && (y = __KB_PTR(b, x)[i - 1])->n == b->t - 1) { \
+				__KB_KEY(key_t, y)[y->n++] = __KB_KEY(key_t, x)[i - 1];	\
+				memmove(__KB_KEY(key_t, y) + y->n, __KB_KEY(key_t, xp), xp->n * sizeof(key_t));	\
+				if (y->is_internal) memmove(__KB_PTR(b, y) + y->n, __KB_PTR(b, xp), (xp->n + 1) * sizeof(void*)); \
+				y->n += xp->n;											\
+				memmove(__KB_KEY(key_t, x) + i - 1, __KB_KEY(key_t, x) + i, (x->n - i) * sizeof(key_t)); \
+				memmove(__KB_PTR(b, x) + i, __KB_PTR(b, x) + i + 1, (x->n - i) * sizeof(void*)); \
+				--x->n;													\
+				free(xp);												\
+				xp = y;													\
+			} else if (i < x->n && (y = __KB_PTR(b, x)[i + 1])->n == b->t - 1) { \
+				__KB_KEY(key_t, xp)[xp->n++] = __KB_KEY(key_t, x)[i];	\
+				memmove(__KB_KEY(key_t, xp) + xp->n, __KB_KEY(key_t, y), y->n * sizeof(key_t));	\
+				if (xp->is_internal) memmove(__KB_PTR(b, xp) + xp->n, __KB_PTR(b, y), (y->n + 1) * sizeof(void*)); \
+				xp->n += y->n;											\
+				memmove(__KB_KEY(key_t, x) + i, __KB_KEY(key_t, x) + i + 1, (x->n - i - 1) * sizeof(key_t)); \
+				memmove(__KB_PTR(b, x) + i + 1, __KB_PTR(b, x) + i + 2, (x->n - i - 1) * sizeof(void*)); \
+				--x->n;													\
+				free(y);												\
+			}															\
+		}																\
+		return __kb_delp_aux_##name(b, xp, k, s);						\
+	}																	\
+	static key_t kb_delp_##name(kbtree_##name##_t *b, const key_t * __restrict k) \
+	{																	\
+		kbnode_t *x;													\
+		key_t ret;														\
+		ret = __kb_delp_aux_##name(b, b->root, k, 0);					\
+		--b->n_keys;													\
+		if (b->root->n == 0 && b->root->is_internal) {					\
+			--b->n_nodes;												\
+			x = b->root;												\
+			b->root = __KB_PTR(b, x)[0];								\
+			free(x);													\
+		}																\
+		return ret;														\
+	}																	\
+	static inline key_t kb_del_##name(kbtree_##name##_t *b, const key_t k) \
+	{																	\
+		return kb_delp_##name(b, &k);									\
+	}
+
+typedef struct {
+	kbnode_t *x;
+	int i;
+} __kbstack_t;
+
+#define __kb_traverse(key_t, b, __func) do {							\
+		int __kmax = 8;													\
+		__kbstack_t *__kstack, *__kp;									\
+		__kp = __kstack = (__kbstack_t*)calloc(__kmax, sizeof(__kbstack_t)); \
+		__kp->x = (b)->root; __kp->i = 0;								\
+		for (;;) {														\
+			while (__kp->x && __kp->i <= __kp->x->n) {					\
+				if (__kp - __kstack == __kmax - 1) {					\
+					__kmax <<= 1;										\
+					__kstack = (__kbstack_t*)realloc(__kstack, __kmax * sizeof(__kbstack_t)); \
+					__kp = __kstack + (__kmax>>1) - 1;					\
+				}														\
+				(__kp+1)->i = 0; (__kp+1)->x = __kp->x->is_internal? __KB_PTR(b, __kp->x)[__kp->i] : 0; \
+				++__kp;													\
+			}															\
+			--__kp;														\
+			if (__kp >= __kstack) {										\
+				if (__kp->x && __kp->i < __kp->x->n) __func(&__KB_KEY(key_t, __kp->x)[__kp->i]); \
+				++__kp->i;												\
+			} else break;												\
+		}																\
+		free(__kstack);													\
+	} while (0)
+
+#define KBTREE_INIT(name, key_t, __cmp)			\
+	__KB_TREE_T(name)							\
+	__KB_INIT(name, key_t)						\
+	__KB_GET_AUX1(name, key_t, __cmp)			\
+	__KB_GET(name, key_t)						\
+	__KB_INTERVAL(name, key_t)					\
+	__KB_PUT(name, key_t, __cmp)				\
+	__KB_DEL(name, key_t)
+
+#define KB_DEFAULT_SIZE 512
+
+#define kbtree_t(name) kbtree_##name##_t
+#define kb_init(name, s) kb_init_##name(s)
+#define kb_destroy(name, b) __kb_destroy(b)
+#define kb_get(name, b, k) kb_get_##name(b, k)
+#define kb_put(name, b, k) kb_put_##name(b, k)
+#define kb_del(name, b, k) kb_del_##name(b, k)
+#define kb_interval(name, b, k, l, u) kb_interval_##name(b, k, l, u)
+#define kb_getp(name, b, k) kb_getp_##name(b, k)
+#define kb_putp(name, b, k) kb_putp_##name(b, k)
+#define kb_delp(name, b, k) kb_delp_##name(b, k)
+#define kb_intervalp(name, b, k, l, u) kb_intervalp_##name(b, k, l, u)
+
+#define kb_size(b) ((b)->n_keys)
+
+#define kb_generic_cmp(a, b) (((b) < (a)) - ((a) < (b)))
+#define kb_str_cmp(a, b) strcmp(a, b)
+
+#endif