diff --git a/src/parse/formulas.rs b/src/parse/formulas.rs
index 5a22b98..b13bb57 100644
--- a/src/parse/formulas.rs
+++ b/src/parse/formulas.rs
@@ -506,17 +506,17 @@ mod tests
 			_ => panic!("expected predicate"),
 		};
 
-		assert_eq!(format_formula("true  and  false"), "true and false");
-		assert_eq!(formula_as_and("true and false").len(), 2);
-		assert_eq!(*formula_as_and("true and false").remove(0), Formula::true_());
-		assert_eq!(*formula_as_and("true and false").remove(1), Formula::false_());
+		assert_eq!(format_formula("(true  and  false)"), "true and false");
+		assert_eq!(formula_as_and("(true and false)").len(), 2);
+		assert_eq!(*formula_as_and("(true and false)").remove(0), Formula::true_());
+		assert_eq!(*formula_as_and("(true and false)").remove(1), Formula::false_());
 		// The order of elements is retained
-		assert_ne!(formula("true and false"), formula("false and true"));
-		assert_eq!(format_formula("p  and  q  and  r  and  s"), "p and q and r and s");
+		assert_ne!(formula("(true and false)"), formula("false and true"));
+		assert_eq!(format_formula("(p  and  q  and  r  and  s)"), "p and q and r and s");
 		assert_eq!(
-			as_predicate(*formula_as_and("p and q and r and s").remove(0)).declaration.name, "p");
+			as_predicate(*formula_as_and("(p and q and r and s)").remove(0)).declaration.name, "p");
 		assert_eq!(
-			as_predicate(*formula_as_and("p and q and r and s").remove(3)).declaration.name, "s");
+			as_predicate(*formula_as_and("(p and q and r and s)").remove(3)).declaration.name, "s");
 
 		let formula = |i| original::formula(i, &Declarations::new());
 
@@ -546,17 +546,17 @@ mod tests
 			_ => panic!("expected predicate"),
 		};
 
-		assert_eq!(format_formula("true  or  false"), "true or false");
-		assert_eq!(formula_as_or("true or false").len(), 2);
-		assert_eq!(*formula_as_or("true or false").remove(0), Formula::true_());
-		assert_eq!(*formula_as_or("true or false").remove(1), Formula::false_());
+		assert_eq!(format_formula("(true  or  false)"), "true or false");
+		assert_eq!(formula_as_or("(true or false)").len(), 2);
+		assert_eq!(*formula_as_or("(true or false)").remove(0), Formula::true_());
+		assert_eq!(*formula_as_or("(true or false)").remove(1), Formula::false_());
 		// The order of elements is retained
-		assert_ne!(formula("true or false"), formula("false or true"));
-		assert_eq!(format_formula("p  or  q  or  r  or  s"), "p or q or r or s");
+		assert_ne!(formula("(true or false)"), formula("false or true)"));
+		assert_eq!(format_formula("(p  or  q  or  r  or  s)"), "p or q or r or s");
 		assert_eq!(
-			as_predicate(*formula_as_or("p or q or r or s").remove(0)).declaration.name, "p");
+			as_predicate(*formula_as_or("(p or q or r or s)").remove(0)).declaration.name, "p");
 		assert_eq!(
-			as_predicate(*formula_as_or("p or q or r or s").remove(3)).declaration.name, "s");
+			as_predicate(*formula_as_or("(p or q or r or s)").remove(3)).declaration.name, "s");
 
 		let formula = |i| original::formula(i, &Declarations::new());