Function prove_tx 

pub fn prove_tx<P, E>(
    params: &Parameters<E>,
    pool_params: &P,
    transfer_pub: TransferPub<E::Fr>,
    transfer_sec: TransferSec<E::Fr>,
) -> (Vec<Num<E::Fr>>, Proof<E>)
where
    P: PoolParams<Fr = E::Fr>,
    E: Engine,