@classmethod
def init_cli(cls):
    """Initialize swipl if it was not initialized yet"""
    from . import Trial
    if not cls.prolog_cli:
        from pyswip import Prolog
        cls.prolog_cli = Prolog()
        cls.prolog_cli.assertz(Trial.prolog_description.empty()[:-1])
        cls.prolog_cli.assertz('load_rules(0)')
