diff --git a/CreuSAT/src/logic/logic.rs b/CreuSAT/src/logic/logic.rs
index 8cc03af9..0bd9d0d9 100644
--- a/CreuSAT/src/logic/logic.rs
+++ b/CreuSAT/src/logic/logic.rs
@@ -1,4 +1,3 @@
-extern crate creusot_contracts;
 use creusot_contracts::std::*;
 use creusot_contracts::*;
 
@@ -6,6 +5,42 @@ use crate::{assignments::*, clause::*, formula::*, lit::*, trail::*};
 
 use crate::logic::{logic_assignments::*, logic_clause::*, logic_formula::*, logic_trail::*};
 
+#[cfg(feature = "contracts")]
+mod inner {
+    struct Model(Mapping<Int, bool>);
+
+    impl Model {
+        #[predicate]
+        fn satisfies_clause(self, cl: Seq<Lit>) -> bool {
+            pearlite! {
+                forall<i : _> 0 <= i && i < cl.len() ==> self.get(@cl[i].idx) == cl[i].polarity
+            }
+        }
+
+        #[predicate]
+        fn satisfies(self, fml: Seq<Seq<Lit>>) -> bool {
+            pearlite! {
+                forall<c : _> 0 <= i && i < fml.len() ==> self.satisfies_clause(fml[c])
+            }
+        }
+    }
+
+    impl Formula {
+        #[predicate]
+        fn unsat(self) -> bool {
+            pearlite! { forall<m : Model> m.satisfies(@self) ==> false }
+        }
+
+        #[predicate]
+        fn sat(self) -> bool {
+            pearlite! { exists<m : Model> m.satisfies(@self) }
+        }
+    }
+}
+
+#[cfg(feature = "contracts")]
+pub use inner::*;
+
 #[logic]
 fn pos() -> AssignedState {
     1u8