Warning: No rules/facts defined for relation A in file empty_relations.dl at line 5
.decl A(x:number)
------^-----------
Warning: Variable x only occurs once in file empty_relations.dl at line 7
B(1) :- A(x).
----------^---
Warning: No rules/facts defined for relation C in file empty_relations.dl at line 14
.decl C(x:number)
------^-----------
Warning: Variable x only occurs once in file empty_relations.dl at line 19
    D(1) :- C(x).
--------------^---
