Inference example:

Given
airport_kb = kb.from_facts([
    ('is', 'N29EO', 'Plane'),
    ('at', 'N29EO', 'dia'),
    ('is', 'N10IV', 'Plane'),
    ('at', 'N10IV', 'oak'),
    ('is', 'N33FR', 'Plane'),
    ('at', 'N33FR', 'lga'),
    ('is', 'dia', 'Airport'),
    ('is', 'lga', 'Airport'),
    ('is', 'oak', 'Airport'),
])

fly = actions.Action(
    [('is', '?subject', 'Plane'), ('is', '?object', 'Airport')],
    [('at', '?subject', '?object'),],
    [('at', '?subject', '?current'),],
    [('at', '?subject', '?object')])

Should be able to do something like:
> infer(airport_kb, [fly], ('at', 'N10IV', 'lga'))
('fly', 'N10IV', 'lga')


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Inference search example:

airport_kb = [
    ('is', 'N29EO', 'Plane'),
    ('at', 'N29EO', 'dia'),
    ('is', 'N10IV', 'Plane'),
    ('at', 'N10IV', 'oak'),
    ('is', 'N33FR', 'Plane'),
    ('at', 'N33FR', 'lga'),
    ('is', '1Z12345E0205271688', 'Package'),
    ('at', '1Z12345E0205271688', 'dia'),
    ('is', '1Z12345E6605272234', 'Package'),
    ('at', '1Z12345E6605272234', 'dia'),
    ('is', '1Z12345E0305271640', 'Package'),
    ('at', '1Z12345E0305271640', 'oak'),
    ('is', '1Z12345E1305277940', 'Package'),
    ('at', '1Z12345E1305277940', 'lga'),
    ('is', '1Z12345E6205277936', 'Package'),
    ('at', '1Z12345E6205277936', 'lga'),
    ('is', 'dia', 'Airport'),
    ('is', 'lga', 'Airport'),
    ('is', 'oak', 'Airport'),
]

fly = actions.Action(
    [('is', '?subject', 'Plane'), ('is', '?object', 'Airport')],
    [('at', '?subject', '?object'),],
    [('at', '?subject', '?current'),],
    [('at', '?subject', '?object')])

Trying to define load which requires that both package and airplane are
at the same place: how can this be expressed?