in src/node_template.rs [237:242]
fn merge(lch: &HashWiresNodeSmt<D>, rch: &HashWiresNodeSmt<D>) -> HashWiresNodeSmt<D> {
let mut hasher = D::new();
hasher.update(&lch.hash);
hasher.update(&rch.hash);
HashWiresNodeSmt::new(hasher.finalize().to_vec())
}