I am trying to reproduce the examples in The Reasoned Schemer using kanren, and example 45 ("a variable cannot be equal to a list in which it occurs") hangs:

from kanren import var, run, eq

run(1, q, eq((q,), q))
# expected the empty tuple ()

The following also hangs:

from cons import cons
from kanren import var, run, eq

run(1, q, eq(cons(q, ()), q))
# expected an empty tuple

I am not sure this is a bug, so posting before investigating further.