def issue_tranche(tx, issuer_pseudonym, asset_name, quantity, tranche_seniority):
    # Need to figure out how we want to determine
    existing_asset_tranche = CALL('get_asset_tranche', 'asset_name', 'tranche_seniority')

    # If no tranche has ever been issued
    if existing_asset is None:
        # Create asset with 0 quantity (has to be better way to do this!
        existing_asset = CALL('issuances.issue'(tx, issuer_pseudonym, asset_name, 0)
        existing_asset['tranche_seniority'] = (tranche_seniority, quantity)

    # If `tranche_seniority` has never been issued
    elif existing_asset['tranche_seniority'] == None:
        # Create tranche
        if existing_asset['issuer'] != issuer_pseudonym:
            raise ERROR('asset issued by another pseudonym')
        existing_asset['tranche_seniority'] = tranche_seniority
        existing_asset['quantity'] = quantity

    # If asset has tranche has already been issued, check approvals and then increase quantity.

@importable
@queryable
def get_tranche(asset, tranche_seniority):
        return STORAGE['asset', asset]
        return STORAGE['tranche_seniority', tranche_seniority]