def statement_base_verb(stmt_type):
    """Return the base verb form of a statement type.

    Parameters
    ----------
    stmt_type : str
        The lower case string form of a statement type, for instance,
        'phosphorylation'.

    Returns
    -------
    str
        The base verb form of a statement type, for instance, 'phosphorylate'.
    """
    override = {'complex': 'bind', 'regulateamount':
        'regulate the amount of', 'increaseamount':
        'increase the amount of', 'decreaseamount':
        'decrease the amount of', 'gef': 'act as a GEF for', 'gap':
        'act as a GAP for', 'inhibition': 'inhibit', 'gtpactivation':
        'activate when bound to GTP', 'regulateactivity':
        'regulate the activity of', 'activeform': 'have active form',
        'conversion': 'convert', 'influence': 'influence', 'modification':
        'modify', 'addmodification': 'add a modification to',
        'removemodification': 'remove a modification of',
        'selfmodification': 'modify itself', 'event': 'happen'}
    return override.get(stmt_type) if stmt_type in override else stmt_type[:-3
        ] + 'e'
