diff --git a/src/account.rs b/src/account.rs
index 7b5bd1908..657f1d23b 100644
--- a/src/account.rs
+++ b/src/account.rs
@@ -1,12 +1,4 @@
-use std::collections::HashMap;
-use util::hash::*;
-use util::sha3::*;
-use util::hashdb::*;
-use util::bytes::*;
-use util::trie::*;
-use util::rlp::*;
-use util::uint::*;
-use std::cell::*;
+use util::*;
 
 pub const SHA3_EMPTY: H256 = H256( [0xc5, 0xd2, 0x46, 0x01, 0x86, 0xf7, 0x23, 0x3c, 0x92, 0x7e, 0x7d, 0xb2, 0xdc, 0xc7, 0x03, 0xc0, 0xe5, 0x00, 0xb6, 0x53, 0xca, 0x82, 0x27, 0x3b, 0x7b, 0xfa, 0xd8, 0x04, 0x5d, 0x85, 0xa4, 0x70] );
 
@@ -66,7 +58,7 @@ impl Account {
 	}
 
 	/// Create a new contract account.
-	/// NOTE: make sure you use `set_code` on this before `commit`ing.
+	/// NOTE: make sure you use `init_code` on this before `commit`ing.
 	pub fn new_contract(balance: U256) -> Account {
 		Account {
 			balance: balance,
@@ -80,7 +72,7 @@ impl Account {
 
 	/// Set this account's code to the given code.
 	/// NOTE: Account should have been created with `new_contract`.
-	pub fn set_code(&mut self, code: Bytes) {
+	pub fn init_code(&mut self, code: Bytes) {
 		assert!(self.code_hash.is_none());
 		self.code_cache = code;
 	}
@@ -224,7 +216,7 @@ fn storage_at() {
 		let mut a = Account::new_contract(U256::from(69u8));
 		a.set_storage(H256::from(&U256::from(0x00u64)), H256::from(&U256::from(0x1234u64)));
 		a.commit_storage(&mut db);
-		a.set_code(vec![]);
+		a.init_code(vec![]);
 		a.commit_code(&mut db);
 		a.rlp()
 	};
@@ -241,7 +233,7 @@ fn note_code() {
 
 	let rlp = {
 		let mut a = Account::new_contract(U256::from(69u8));
-		a.set_code(vec![0x55, 0x44, 0xffu8]);
+		a.init_code(vec![0x55, 0x44, 0xffu8]);
 		a.commit_code(&mut db);
 		a.rlp()
 	};
@@ -267,7 +259,7 @@ fn commit_storage() {
 fn commit_code() {
 	let mut a = Account::new_contract(U256::from(69u8));
 	let mut db = OverlayDB::new_temp();
-	a.set_code(vec![0x55, 0x44, 0xffu8]);
+	a.init_code(vec![0x55, 0x44, 0xffu8]);
 	assert_eq!(a.code_hash(), SHA3_EMPTY);
 	a.commit_code(&mut db);
 	assert_eq!(a.code_hash().hex(), "af231e631776a517ca23125370d542873eca1fb4d613ed9b5d5335a46ae5b7eb");
diff --git a/src/block.rs b/src/block.rs
index b1ebece79..ae05cc94d 100644
--- a/src/block.rs
+++ b/src/block.rs
@@ -1,9 +1,4 @@
-use std::collections::hash_set::*;
-use util::hash::*;
-use util::bytes::*;
-use util::uint::*;
-use util::error::*;
-use util::overlaydb::*;
+use util::*;
 use transaction::*;
 use receipt::*;
 use blockchain::*;
diff --git a/src/blockchain.rs b/src/blockchain.rs
index df729787a..399a8b330 100644
--- a/src/blockchain.rs
+++ b/src/blockchain.rs
@@ -1,18 +1,7 @@
 //! Fast access to blockchain data.
 
-use std::collections::HashMap;
-use std::cell::RefCell;
-use std::path::Path;
-use std::hash::Hash;
+use util::*;
 use rocksdb::{DB, WriteBatch, Writable};
-use heapsize::HeapSizeOf;
-use util::hash::*;
-use util::uint::*;
-use util::rlp::*;
-use util::hashdb::*;
-use util::sha3::*;
-use util::bytes::*;
-use util::squeeze::*;
 use header::*;
 use extras::*;
 use transaction::*;
diff --git a/src/builtin.rs b/src/builtin.rs
index ade5aa8d2..7f8f0690b 100644
--- a/src/builtin.rs
+++ b/src/builtin.rs
@@ -1,12 +1,4 @@
-use std::cmp::min;
-use std::fmt;
-use util::uint::*;
-use util::hash::*;
-use util::sha3::*;
-use util::bytes::*;
-use rustc_serialize::json::Json;
-use std::io::Write;
-use util::crypto::*;
+use util::*;
 use crypto::sha2::Sha256;
 use crypto::ripemd160::Ripemd160;
 use crypto::digest::Digest;
@@ -95,8 +87,8 @@ pub fn new_builtin_exec(name: &str) -> Option<Box<Fn(&[u8], &mut [u8])>> {
 			it.copy_raw(input);
 			if it.v == H256::from(&U256::from(27)) || it.v == H256::from(&U256::from(28)) {
 				let s = Signature::from_rsv(&it.r, &it.s, it.v[31] - 27);
-				if is_valid(&s) {
-					match recover(&s, &it.hash) {
+				if ec::is_valid(&s) {
+					match ec::recover(&s, &it.hash) {
 						Ok(p) => {
 							let r = p.as_slice().sha3();
 							// NICE: optimise and separate out into populate-like function
diff --git a/src/common.rs b/src/common.rs
new file mode 100644
index 000000000..bc6371abf
--- /dev/null
+++ b/src/common.rs
@@ -0,0 +1,9 @@
+pub use util::*;
+pub use env_info::*;
+pub use evm_schedule::*;
+pub use denominations::*;
+pub use views::*;
+pub use builtin::*;
+pub use header::*;
+pub use account::*;
+pub use transaction::*;
diff --git a/src/denominations.rs b/src/denominations.rs
index 183e89f26..a23c94b4c 100644
--- a/src/denominations.rs
+++ b/src/denominations.rs
@@ -1,4 +1,4 @@
-use util::uint::*;
+use util::*;
 
 #[inline]
 pub fn ether() -> U256 { U256::exp10(18) }
diff --git a/src/engine.rs b/src/engine.rs
index aec721818..318c5a6b4 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -1,16 +1,6 @@
-use std::collections::hash_map::*;
-use util::bytes::*;
-use util::hash::*;
-use util::uint::*;
-use util::rlp::*;
-use util::semantic_version::*;
-use util::error::*;
-use header::Header;
-use transaction::Transaction;
+use common::*;
 use block::Block;
 use spec::Spec;
-use evm_schedule::EvmSchedule;
-use env_info::EnvInfo;
 
 /// A consensus mechanism for the chain. Generally either proof-of-work or proof-of-stake-based.
 /// Provides hooks into each of the major parts of block import.
diff --git a/src/env_info.rs b/src/env_info.rs
index dec8069ac..919db314d 100644
--- a/src/env_info.rs
+++ b/src/env_info.rs
@@ -1,5 +1,4 @@
-use util::uint::*;
-use util::hash::*;
+use util::*;
 
 /// Simple vector of hashes, should be at most 256 items large, can be smaller if being used
 /// for a block whose number is less than 257.
diff --git a/src/ethash.rs b/src/ethash.rs
index f2d1320c5..219d0f870 100644
--- a/src/ethash.rs
+++ b/src/ethash.rs
@@ -1,10 +1,7 @@
-//use util::error::*;
-use util::rlp::decode;
-use engine::Engine;
-use spec::Spec;
+use common::*;
 use block::*;
-use evm_schedule::EvmSchedule;
-use env_info::EnvInfo;
+use spec::*;
+use engine::*;
 
 /// Engine using Ethash proof-of-work consensus algorithm, suitable for Ethereum
 /// mainnet chains in the Olympic, Frontier and Homestead eras.
@@ -31,3 +28,13 @@ impl Engine for Ethash {
 }
 
 // TODO: test for on_close_block.
+#[test]
+fn playpen() {
+	use util::sha3::*;
+	use util::overlaydb::*;
+	let engine = Spec::new_morden().to_engine().unwrap();
+	let genesis_header = engine.spec().genesis_header();
+	let mut db = OverlayDB::new_temp();
+	engine.spec().ensure_db_good(&mut db);
+	let b = OpenBlock::new(engine.deref(), db, &genesis_header, vec![genesis_header.hash()]);
+}
\ No newline at end of file
diff --git a/src/extras.rs b/src/extras.rs
index 93144dda7..39ce814c8 100644
--- a/src/extras.rs
+++ b/src/extras.rs
@@ -1,8 +1,5 @@
-use heapsize::HeapSizeOf;
+use util::*;
 use rocksdb::{DB, Writable};
-use util::uint::*;
-use util::hash::*;
-use util::rlp::*;
 
 /// Represents index of extra data in database
 #[derive(Copy, Clone)]
diff --git a/src/genesis.rs b/src/genesis.rs
index 63a0caf81..aa6897573 100644
--- a/src/genesis.rs
+++ b/src/genesis.rs
@@ -1,14 +1,5 @@
-use std::io::Read;
-use std::str::FromStr;
-use std::collections::HashMap;
-use rustc_serialize::base64::FromBase64;
-use rustc_serialize::json::Json;
-use rustc_serialize::hex::FromHex;
+use util::*;
 use flate2::read::GzDecoder;
-use util::rlp::*;
-use util::hash::*;
-use util::uint::*;
-use util::sha3::*;
 use account::*;
 use header::*;
 
@@ -90,7 +81,8 @@ impl Genesis {
 				let mixhash = H256::from_str(&json["mixhash"].as_string().unwrap()[2..]).unwrap();
 				let nonce = H64::from_str(&json["nonce"].as_string().unwrap()[2..]).unwrap();
 				vec![encode(&mixhash), encode(&nonce)]
-			}
+			},
+			hash: RefCell::new(None),
 		};
 		
 		(header, state)
diff --git a/src/header.rs b/src/header.rs
index ab84d5c58..80d91eb20 100644
--- a/src/header.rs
+++ b/src/header.rs
@@ -1,7 +1,4 @@
-use util::hash::*;
-use util::bytes::*;
-use util::uint::*;
-use util::rlp::*;
+use util::*;
 
 /// Type for a 2048-bit log-bloom, as used by our blocks.
 pub type LogBloom = H2048;
@@ -38,6 +35,8 @@ pub struct Header {
 
 	pub difficulty: U256,
 	pub seal: Vec<Bytes>,
+
+	pub hash: RefCell<Option<H256>>, //TODO: make this private
 }
 
 impl Header {
@@ -61,6 +60,21 @@ impl Header {
 
 			difficulty: ZERO_U256.clone(),
 			seal: vec![],
+			hash: RefCell::new(None),
+		}
+	}
+
+	pub fn hash(&self) -> H256 {
+ 		let mut hash = self.hash.borrow_mut();
+ 		match &mut *hash {
+ 			&mut Some(ref h) => h.clone(),
+ 			hash @ &mut None => {
+ 				let mut stream = RlpStream::new();
+ 				stream.append(self);
+ 				let h = stream.as_raw().sha3();
+ 				*hash = Some(h.clone());
+ 				h.clone()
+ 			}
 		}
 	}
 }
@@ -84,6 +98,7 @@ impl Decodable for Header {
 			timestamp: try!(Decodable::decode(&d[11])),
 			extra_data: try!(Decodable::decode(&d[12])),
 			seal: vec![],
+			hash: RefCell::new(None),
 		};
 
 		for i in 13..d.len() {
diff --git a/src/lib.rs b/src/lib.rs
index 054947ebe..9c2bd2d1d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -84,11 +84,7 @@ extern crate env_logger;
 extern crate evmjit;
 extern crate ethcore_util as util;
 
-//use util::error::*;
-pub use util::hash::*;
-pub use util::uint::*;
-pub use util::bytes::*;
-
+pub mod common;
 pub mod env_info;
 pub mod engine;
 pub mod state;
diff --git a/src/receipt.rs b/src/receipt.rs
index 481b6eda0..fb72e2e18 100644
--- a/src/receipt.rs
+++ b/src/receipt.rs
@@ -1,5 +1,4 @@
-use util::hash::*;
-use util::uint::*;
+use util::*;
 
 /// Information describing execution of a transaction.
 pub struct Receipt {
diff --git a/src/spec.rs b/src/spec.rs
index eee653966..a3fafa60f 100644
--- a/src/spec.rs
+++ b/src/spec.rs
@@ -1,25 +1,8 @@
-use std::io::Read;
-use std::collections::HashMap;
-use std::cell::*;
-use std::str::FromStr;
-use rustc_serialize::base64::FromBase64;
-use rustc_serialize::json::Json;
-use rustc_serialize::hex::FromHex;
+use common::*;
 use flate2::read::GzDecoder;
-use util::uint::*;
-use util::hash::*;
-use util::bytes::*;
-use util::triehash::*;
-use util::error::*;
-use util::rlp::*;
-use util::sha3::*;
-use account::*;
-use engine::Engine;
-use builtin::Builtin;
-use null_engine::NullEngine;
-use ethash::Ethash;
-use denominations::*;
-use header::*;
+use engine::*;
+use null_engine::*;
+use ethash::*;
 
 /// Converts file from base64 gzipped bytes to json
 pub fn gzip64res_to_json(source: &[u8]) -> Json {
@@ -107,7 +90,7 @@ impl Spec {
 		Ref::map(self.state_root_memo.borrow(), |x|x.as_ref().unwrap())
 	}
 
-	fn genesis_header(&self) -> Header {
+	pub fn genesis_header(&self) -> Header {
 		Header {
 			parent_hash: self.parent_hash.clone(),
 			timestamp: self.timestamp.clone(),
@@ -129,8 +112,9 @@ impl Spec {
 					s.out()
 				};
 				let r = Rlp::new(&seal);
-				(0..self.seal_fields).map(|i| r.at(i).raw().to_vec()).collect()
+				(0..self.seal_fields).map(|i| r.at(i).as_raw().to_vec()).collect()
 			},
+			hash: RefCell::new(None),
 		}
 	}
 
@@ -342,6 +326,17 @@ impl Spec {
 		}
 	}
 
+	/// Ensure that the given state DB has the trie nodes in for the genesis state.
+	pub fn ensure_db_good(&self, db: &mut HashDB) {
+		if !db.contains(&self.state_root()) {
+			let mut root = H256::new();
+			let mut t = SecTrieDBMut::new(db, &mut root);
+			for (address, account) in self.genesis_state.iter() {
+				t.insert(address.as_slice(), &account.rlp());
+			}
+		}
+	}
+
 	/// Create a new Spec from a JSON UTF-8 data resource `data`.
 	pub fn from_json_utf8(data: &[u8]) -> Spec {
 		Self::from_json_str(::std::str::from_utf8(data).unwrap())
@@ -365,26 +360,16 @@ mod tests {
 	use std::str::FromStr;
 	use util::hash::*;
 	use util::sha3::*;
-	use rustc_serialize::json::Json;
 	use views::*;
 	use super::*;
 
-	#[test]
-	fn morden_manual() {
-		let morden = Spec::new_morden_manual();
-
-		assert_eq!(*morden.state_root(), H256::from_str("f3f4696bbf3b3b07775128eb7a3763279a394e382130f27c21e70233e04946a9").unwrap());
-		let genesis = morden.genesis_block();
-		assert_eq!(BlockView::new(&genesis).header_view().sha3(), H256::from_str("0cd786a2425d16f152c658316c423e6ce1181e15c3295826d7c9904cba9ce303").unwrap());
-	}
-
 	#[test]
 	fn morden() {
-		let morden = Spec::new_morden();
-
-		assert_eq!(*morden.state_root(), H256::from_str("f3f4696bbf3b3b07775128eb7a3763279a394e382130f27c21e70233e04946a9").unwrap());
-		let genesis = morden.genesis_block();
-		assert_eq!(BlockView::new(&genesis).header_view().sha3(), H256::from_str("0cd786a2425d16f152c658316c423e6ce1181e15c3295826d7c9904cba9ce303").unwrap());
+		for morden in [Spec::new_morden(), Spec::new_morden_manual()].into_iter() {
+			assert_eq!(*morden.state_root(), H256::from_str("f3f4696bbf3b3b07775128eb7a3763279a394e382130f27c21e70233e04946a9").unwrap());
+			let genesis = morden.genesis_block();
+			assert_eq!(BlockView::new(&genesis).header_view().sha3(), H256::from_str("0cd786a2425d16f152c658316c423e6ce1181e15c3295826d7c9904cba9ce303").unwrap());
+		}
 	}
 
 	#[test]
diff --git a/src/state.rs b/src/state.rs
index 019dc0426..80c8276fc 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -1,14 +1,4 @@
-use std::cell::*;
-use std::ops::*;
-use std::collections::HashMap;
-use util::hash::*;
-use util::hashdb::*;
-use util::overlaydb::*;
-use util::trie::*;
-use util::bytes::*;
-use util::rlp::*;
-use util::uint::*;
-use util::error::*;
+use util::*;
 use account::Account;
 use transaction::Transaction;
 use receipt::Receipt;
@@ -129,9 +119,10 @@ impl State {
 		self.require(a, false).set_storage(key, value);
 	}
 
-	/// Mutate storage of account `a` so that it is `value` for `key`.
-	pub fn set_code(&mut self, a: &Address, code: Bytes) {
-		self.require_or_from(a, true, || Account::new_contract(U256::from(0u8))).set_code(code);
+	/// Initialise the code of account `a` so that it is `value` for `key`.
+	/// NOTE: Account should have been created with `new_contract`.
+	pub fn init_code(&mut self, a: &Address, code: Bytes) {
+		self.require_or_from(a, true, || Account::new_contract(U256::from(0u8))).init_code(code);
 	}
 
 	/// Execute a given transaction.
@@ -238,7 +229,7 @@ fn code_from_database() {
 	let (r, db) = {
 		let mut s = State::new_temp();
 		s.require_or_from(&a, false, ||Account::new_contract(U256::from(42u32)));
-		s.set_code(&a, vec![1, 2, 3]);
+		s.init_code(&a, vec![1, 2, 3]);
 		assert_eq!(s.code(&a), Some([1u8, 2, 3].to_vec()));
 		s.commit();
 		assert_eq!(s.code(&a), Some([1u8, 2, 3].to_vec()));
diff --git a/src/transaction.rs b/src/transaction.rs
index d24448c93..b54329422 100644
--- a/src/transaction.rs
+++ b/src/transaction.rs
@@ -1,7 +1,4 @@
-use util::hash::*;
-use util::bytes::*;
-use util::uint::*;
-use util::rlp::*;
+use util::*;
 
 /// A set of information describing an externally-originating message call
 /// or contract creation operation.
diff --git a/src/views.rs b/src/views.rs
index e8425cc17..e66a46178 100644
--- a/src/views.rs
+++ b/src/views.rs
@@ -1,9 +1,5 @@
 //! Block oriented views onto rlp.
-use util::bytes::*;
-use util::hash::*;
-use util::uint::*;
-use util::rlp::*;
-use util::sha3::*;
+use util::*;
 use header::*;
 use transaction::*;
 
@@ -49,7 +45,7 @@ impl<'a> BlockView<'a> {
 
 	/// Return transaction hashes.
 	pub fn transaction_hashes(&self) -> Vec<H256> { 
-		self.rlp.at(1).iter().map(|rlp| rlp.raw().sha3()).collect()
+		self.rlp.at(1).iter().map(|rlp| rlp.as_raw().sha3()).collect()
 	}
 
 	/// Return list of uncles of given block.
@@ -59,7 +55,7 @@ impl<'a> BlockView<'a> {
 
 	/// Return list of uncle hashes of given block.
 	pub fn uncle_hashes(&self) -> Vec<H256> { 
-		self.rlp.at(2).iter().map(|rlp| rlp.raw().sha3()).collect()
+		self.rlp.at(2).iter().map(|rlp| rlp.as_raw().sha3()).collect()
 	}
 }
 
@@ -143,6 +139,6 @@ impl<'a> HeaderView<'a> {
 
 impl<'a> Hashable for HeaderView<'a> {
 	fn sha3(&self) -> H256 {
-		self.rlp.raw().sha3()
+		self.rlp.as_raw().sha3()
 	}
 }