(decl pure partial A (u32 u32) u32)
(extern constructor A A)

(decl B (u32 u32) u32)
(extern extractor B B)

(decl partial C (u32 u32 u32 u32) u32)

(decl pure predicate () u32)
(rule (predicate) 1)

(rule 2 (C a b c (B d e))
      (if-let (B f g) d)
      (if-let h (A a b))
      (A h a))

(rule (C a b c d)
      (if (predicate))
      42)

(rule 1 (C a b a b)
      (if-let x (D a b))
      x)

(decl pure D (u32 u32) u32)
(rule (D x 0) x)
(rule 1 (D 0 x) x)