code: func SigncryptSeal(plaintext []byte, ephemeralKeyCreator EphemeralKeyCreator, sender SigningSecretKey, receiverBoxKeys []BoxPublicKey, receiverSymmetricKeys []ReceiverSymmetricKey) (out []byte, err error) {
  	return signcryptSeal(plaintext, sender, receiverBoxKeys, receiverSymmetricKeys, ephemeralKeyCreator, defaultSigncryptRNG{})
  }
docs: // SigncryptSeal a plaintext from the given sender, for the specified
  // receiver groups.  Returns a ciphertext, or an error if something
  // bad happened.
  //
  // ephemeralKeyCreator should be the last argument; it's the 2nd one
  // to preserve the public API.