Neq not working

Hi, with the next code I expected [{'X': '5'}], but it returns ['No']:

```Python
import pytholog as pl
reglas = pl.KnowledgeBase("reglas")
reglas([ 
    "sol(3)",
    "sol(5)",
    "output(A) :- sol(A), B is 3, neq(A, B)"
])    
print(reglas.query(pl.Expr("output(X)")))
```

Thanks a lot.