check precondition
check precondition

jnnk/pyethereum,karlfloersch/pyethereum,vaporry/pyethereum,shahankhatch/pyethereum,ddworken/pyethereum,ethers/pyethereum,ethermarket/pyethereum,karlfloersch/pyethereum,inzem77/pyethereum,shahankhatch/pyethereum,holiman/pyethereum,pipermerriam/pyethereum,ethereum/pyethereum,harlantwood/pyethereum,pipermerriam/pyethereum,ethereum/pyethereum,ckeenan/pyethereum