Bip39 is not defined https://files.fm/u/2eemhhak2q#design Regardless that it utilizes BIP32 system you are able to nonetheless import BIP39 seeds into Electrum wallet. Also apart from BIp32 There's BIP44 Edition which some wallet use for your generation of seeds. For words that only have 3 letters, there isn't any 4th letter. https://t.me/BIP39_CHAT