Cannot import Join from lnn.

[daisylab]

It's related to:

https://ibm.github.io/LNN/education/examples/reasoning.html#more-complex-reasoning-example

the code is:

from lnn import (Predicate, Variable, Join, And,
                 Exists, Implies, Forall, Model, Fact, World)

model = Model()  # Instantiate a model.
x, y, z, w = map(Variable, ['x', 'y', 'z', 'w'])

# Define and add predicates to the model.
owns = model['owns'] = Predicate('owns', 2)  # binary predicate
missile = model['missile'] = Predicate('missile')
american = model['american'] = Predicate('american')
enemy = model['enemy'] = Predicate('enemy', 2)
hostile = model['hostile'] = Predicate('hostile')
criminal = model['criminal'] = Predicate('criminal')
weapon = model['weapon'] = Predicate('weapon')
sells = model['sells'] = Predicate('sells', 3)  # ternary predicate

# Define and add the background knowledge to  the model.
america_enemies = (
    Forall(x, Implies(enemy(x, (y, 'America')),
                      hostile(x),
                      ),
           world=World.AXIOM)
    )
model.add_knowledge(america_enemies)

# Define queries
query = Exists(x, criminal(x))
model.add_knowledge(query)

# Add facts to model.
model.set_facts({
    owns: {('Nono', 'M1'): Fact.TRUE},
    missile: {'M1': Fact.TRUE},
    american: {'West': Fact.TRUE},
    enemy: {('Nono', 'America'): Fact.TRUE},
})

model.infer()
print(model[query].true_groundings)

and it says

Traceback (most recent call last):
  File "/home/sungjin/home/lnn-examples/complex2.py", line 1, in <module>
    from lnn import (Predicate, Variable, Join, And,
ImportError: cannot import name 'Join' from 'lnn' (/home/sungjin/.virtualenvs/lnn/lib/python3.10/site-packages/lnn/__init__.py)