def split_reversible_reactions(crn):
    """
    Replace every reversible reaction with the two corresponding irreversible
    reactions.
    """
    new = []
    for [r, p, k] in crn:
        assert len(k) == 1 or len(k) == 2
        new.append([r, p])
        if len(k) == 2:
            new.append([p, r])
    return new