diff --git a/src/ast.rs b/src/ast.rs
index 3cb94e0..2514108 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -258,13 +258,13 @@ impl Compare
 
 pub struct Exists
 {
-	pub parameters: VariableDeclarations,
+	pub parameters: std::rc::Rc<VariableDeclarations>,
 	pub argument: Box<Formula>,
 }
 
 impl Exists
 {
-	pub fn new(parameters: VariableDeclarations, argument: Box<Formula>) -> Self
+	pub fn new(parameters: std::rc::Rc<VariableDeclarations>, argument: Box<Formula>) -> Self
 	{
 		Self
 		{
@@ -276,13 +276,13 @@ impl Exists
 
 pub struct ForAll
 {
-	pub parameters: VariableDeclarations,
+	pub parameters: std::rc::Rc<VariableDeclarations>,
 	pub argument: Box<Formula>,
 }
 
 impl ForAll
 {
-	pub fn new(parameters: VariableDeclarations, argument: Box<Formula>) -> Self
+	pub fn new(parameters: std::rc::Rc<VariableDeclarations>, argument: Box<Formula>) -> Self
 	{
 		Self
 		{
@@ -504,7 +504,7 @@ impl Formula
 		Self::Compare(Compare::new(operator, left, right))
 	}
 
-	pub fn exists(parameters: VariableDeclarations, argument: Box<Formula>) -> Self
+	pub fn exists(parameters: std::rc::Rc<VariableDeclarations>, argument: Box<Formula>) -> Self
 	{
 		Self::Exists(Exists::new(parameters, argument))
 	}
@@ -519,7 +519,7 @@ impl Formula
 		Self::boolean(false)
 	}
 
-	pub fn for_all(parameters: VariableDeclarations, argument: Box<Formula>) -> Self
+	pub fn for_all(parameters: std::rc::Rc<VariableDeclarations>, argument: Box<Formula>) -> Self
 	{
 		Self::ForAll(ForAll::new(parameters, argument))
 	}