Function hash_h_into 

pub fn hash_h_into<P: Params>(
    pk_seed: &[u8],
    adrs: &Adrs,
    m1: &[u8],
    m2: &[u8],
    out: &mut [u8],
)

H(PK.seed, ADRS, M1 || M2) — two-input Merkle node hash. Output to out (n bytes).