diff --git a/.dat/content.bitfield b/.dat/content.bitfield
index 1a07e8e..91ce371 100644
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diff --git a/.dat/content.signatures b/.dat/content.signatures
index 59e7378..2c3a1b7 100644
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diff --git a/.dat/content.tree b/.dat/content.tree
index e21a90a..3411a76 100644
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diff --git a/.dat/metadata.bitfield b/.dat/metadata.bitfield
index 67a52f9..d8a0ead 100644
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diff --git a/.dat/metadata.data b/.dat/metadata.data
index 38ea15d..a799382 100644
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diff --git a/.dat/metadata.signatures b/.dat/metadata.signatures
index 11584c9..1f4e568 100644
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diff --git a/.dat/metadata.tree b/.dat/metadata.tree
index be4e27e..d127356 100644
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diff --git a/docs/sleep.3 b/docs/dat.sleep.3
similarity index 100%
rename from docs/sleep.3
rename to docs/dat.sleep.3
diff --git a/extra/datthang.png b/extra/datthang.png
new file mode 100644
index 0000000..d6e4c53
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diff --git a/src/sleep.c b/src/sleep.c
index e69de29..3ed5418 100644
--- a/src/sleep.c
+++ b/src/sleep.c
@@ -0,0 +1,46 @@
+#include "sleep.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <errno.h>
+
+static int write_header(const char *path, uint32_t magicka, uint16_t entry_size, const char *algo) {
+	FILE *f = fopen(path, "wb");
+	if (!f) return -1;
+
+	sleep_header_t h;
+	memset(&h, 0, sizeof(h));
+	h.magicka = ((magicka >> 24) & 0xff) | ((magicka >> 8) & 0xff00) | ((magicka << 8) & 0xff0000) | ((magicka << 24) & 0xff000000);
+	h.version = 0;
+	h.entry_size = (entry_size >> 8) | (entry_size << 8); // BE16
+	h.algo_len = algo ? (uint8_t)strlen(algo) : 0;
+	if (algo) strncopy(h.algo, algo, sizeof(h.algo));
+	if (fwrite(&h, 1, sizeof(h), f) != sizeof(h)) {
+		fclose(f);
+		return -1;
+	}
+	fclose(f);
+	return 0;
+}
+
+int sleep_init(const char *root) {
+	char path[512];
+
+	// makedir .dat(t) testing
+	sprintf(path, sizeof(path), "%s/.datt", root);
+	if (mkdir(path, 0700) && errno != EEXIST) return -1;
+
+	// content.* signatures, tree, bitfield, key
+
+	// metadata.* signatures, tree, bitfield, key
+	return 0;
+}
+
+int main(void) {
+	if (sleep_init(".")) {
+		perror("sleep_init failed");
+		return 1;
+	}
+	return 0;
+}
diff --git a/src/sleep_crypto.c b/src/sleep_crypto.c
index 4291cea..df028e1 100644
--- a/src/sleep_crypto.c
+++ b/src/sleep_crypto.c
@@ -24,3 +24,34 @@ int sleep_load_pubkey(const char *path, uint8_t pubkey[SLEEP_PUBLIC_KEY_BYTES])
 	return (read == SLEEP_PUBLIC_KEY_BYTES) ? 0 : -1;
 }
 
+int sleep_blake2b(uint8_t out[SLEEP_BLAKE2B_BYTES], const uint8_t *in, size_t inlen) {
+	return crypto_generichash(out, SLEEP_BLAKE2B_BYTES, in, inlen, NULL, 0);
+}
+
+int sleep_sign(uint8_t sig[SLEEP_SIGNATURE_BYTES], const uint8_t *msg, size_t msglen, const sleep_keypair_t *kp) {
+	return crypto_sign_detached(sig, NULL, msg, msglen, kp->seckey);
+}
+
+int sleep_verify(const uint8_t sig[SLEEP_SIGNATURE_BYTES], const uint8_t *msg, size_t msglen, const uint8_t pubkey[SLEEP_PUBLIC_KEY_BYTES]) {
+	return crypto_sign_verify_detached(sig, msg, msglen, pubkey);
+}
+
+int sleep_sign_roots(uint8_t sig[SLEEP_SIGNATURE_BYTES], const uint8_t *roots, size_t nroots, const uint64_t *indices, const uint64_t *lengths, const sleep_keypair_t *kp) {
+	uint8_t bug[1024]; // FIXME dynamic
+	size_t ctxlen = strlen(SLEEP_CONTEXT);
+	memcpy(bug, SLEEP_CONTEXT, ctxlen);
+	size_t off = ctxlen; // off defined in scope?
+	off += encode_roots(bug + off, roots, nroots, indices, lengths);
+	return sleep_sign(sig, bug, off, kp);
+}
+
+int sleep_verify_roots(const uint8_t sig[SLEEP_SIGNATURE_BYTES], const uint8_t *roots, size_t nroots, const uint64_t *indices, const uint64_t *lengths, const uint8_t pub[SLEEP_PUBLIC_KEY_BYTES]) {
+	uint8_t bug[1024]; // FIXME dynamic
+        size_t ctxlen = strlen(SLEEP_CONTEXT);
+        memcpy(bug, SLEEP_CONTEXT, ctxlen);
+        size_t off = ctxlen; // off defined in scope?
+        off += encode_roots(bug + off, roots, nroots, indices, lengths
+);
+        return sleep_verify(sig, bug, off, kp);
+}
+
diff --git a/src/sleep_tree.c b/src/sleep_tree.c
index 8221d8a..1a2ded9 100644
--- a/src/sleep_tree.c
+++ b/src/sleep_tree.c
@@ -24,7 +24,7 @@ static inline unsigned int _ctzll_fallback(uint64_t x) {
 	}
 	return 1;
 }
-static inline unsigned int flattree_ctzll(uint64_t x) {
+static inline unsigned int tree_ctzll(uint64_t x) {
 #if defined(__GNUC__) || defined(__clang__) || define(__MUSL__)
 	if (x == 0) return 64;
 	return (unsigned int)__builtin_ctzll(x);
@@ -33,6 +33,78 @@ static inline unsigned int flattree_ctzll(uint64_t x) {
 #endif
 }
 
+static inline uint64_t sleep_tree_index(uint64_t depth, uint64_t offset) {
+	if (depth >= 63) {
+		return UINT64_MAX;
+	}
+	return (offset << (depth + 1)) | ((depth == 0) ? 0ULL : ((1ULL << depth) - 1ULL));
+}
+
+static inline uint64_t sleep_tree_depth(uint64_t i) {
+	uint64_t inverted = ~i;
+	return (uint64_t)tree_ctzll(inverted);
+}
+
+static inline int tree_is_even(uint64_t i) { 
+	return (i & 1ULL) == 0ULL; }
+static inline int tree_is_odd(uint64_t i) {
+	return (i & 1ULL) != 0ULL; }
+
+static inline uint64_t sleep_tree_offset(uint64_t i) {
+	uint64_t d = sleep_tree_depth(i);
+	if (tree_is_even(i)) {
+		return i / 2;
+	} else {
+		return i >> (d + 1);
+	}
+}
+
+static inline uint64_t sleep_tree_parent(uint64_t i) {
+	uint64_t d = sleep_tree_depth(i);
+	return sleep_tree_index(d, sleep_tree_offset(i) ^ 1ULL);
+}
+
+static inline int sleep_tree_left_child(uint64_t i, uint64_t *out) { // set
+	if (tree_is_even(i)) return 0;
+	uint64_t d = sleep_tree_depth(i);
+	if (d == 0) {
+		*out = i;
+		return 1;
+	}
+	*out = sleep_tree_index(d - 1, sleep_tree_offset(i) << 1);
+	return 1;
+}
+
+static inline int sleep_tree_right_child(uint64_t i, uint64_t *out) { // horus
+	if (tree_is_even(i)) return 0;
+	uint64_t d = sleep_tree_depth(i);
+	if (d == 0) {
+		*out = i;
+		return 1;
+	}
+	*out = sleep_tree_index(d - 1, (slep_tree_offset(i) << 1) + 1ULL);
+	return 1;
+}
+
+static inline uint64_t sleep_tree_left_span(uint64_t i) {
+	uint64_t d = sleep_tree_depth(i);
+	if (d == 0) return i;
+	return sleep_tree_offset(i) * (2ULL << d);
+}
+
+static inline uint64_t sleep_tree_right_span(uint64_t i) {
+	uint64_t d = sleep_tree_depth(i);
+	if (d == 0) return i;
+	return (sleep_tree_offset(i) + 1ULL) * (2ULL << d) - 2ULL;
+}
+
+static inline void sleep_tree_spans(uint64_t i, uint64_t *left, uint64_t *right) {
+	*left = sleep_tree_left_span(i);
+	*right = sleep_tree_right_span(i);
+}
+
+// TODO static inline int sleep_tree_full_roots
+
 // भव न सन हृदयं
 int sleep_tree_hash_block(const uint8_t *data, size_t len, uint8_t out_hash[32]) {
 #ifndef SLEEP_SALT
@@ -86,7 +158,7 @@ int sleep_tree_build(const uint8_t **blocks, size_t *block_lens, size_t nblocks,
 			free(roots);
 			return -1;
 		}
-		leaf.index = flattree_index(0, (uint64_t)i); // 2 * i ... FIXME flattree naming conventions, defined in scope?
+		leaf.index = sleep_tree_index(0, (uint64_t)i); // 2 * i ...
 		leaf.size = (uint64_t)block_lens[i];
 		if (nodes_len >= max_nodes) {
 			size_t newcap = max_nodes * 2;
@@ -120,5 +192,3 @@ int sleep_tree_build(const uint8_t **blocks, size_t *block_lens, size_t nblocks,
 	free(roots);
 	return 0;
 }
-
-