diff --git a/src/main.rs b/src/main.rs
index c0cd556..979382d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,6 @@
 mod rsprocess;
 use lalrpop_util::lalrpop_mod;
+use std::rc::Rc;
 // use std::io;
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
@@ -94,10 +95,10 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let env = grammar::EnvironmentParser::new().parse("[]").unwrap();
     let process = grammar::ContextParser::new().parse("[({a}.nil + {b}.nil),({c}.nil + {d}.nil)]").unwrap();
 
-    let sys = rsprocess::structure::RSsystem::from(*env,
+    let sys = rsprocess::structure::RSsystem::from(Rc::new(*env),
 						   rsprocess::structure::RSset::from(vec![]),
 						   *process,
-						   vec![
+						   Rc::new(vec![
 						       rsprocess::structure::RSreaction::from(
 							   rsprocess::structure::RSset::from(vec!["a"]),
 							   rsprocess::structure::RSset::from(vec!["c"]),
@@ -108,7 +109,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
 							   rsprocess::structure::RSset::from(vec!["d"]),
 							   rsprocess::structure::RSset::from(vec!["b"])
 						       )
-						   ]);
+						   ]));
 
     let it = rsprocess::transitions::iterator_transitions(&sys)?;
 
diff --git a/src/rsprocess/structure.rs b/src/rsprocess/structure.rs
index d7a476c..28b7398 100644
--- a/src/rsprocess/structure.rs
+++ b/src/rsprocess/structure.rs
@@ -267,30 +267,33 @@ impl<'a> From<Vec<(&'a str, RSprocess<'a>)>> for RSenvironment<'a> {
 // -----------------------------------------------------------------------------
 #[derive(Clone, Debug)]
 pub struct RSsystem<'a> {
-    delta: RSenvironment<'a>,
+    delta: Rc<RSenvironment<'a>>,
     available_entities: RSset<'a>,
     context_process: RSprocess<'a>,
-    reaction_rules: Vec<RSreaction<'a>>,
+    reaction_rules: Rc<Vec<RSreaction<'a>>>,
 }
 
 impl<'a> RSsystem<'a> {
     pub fn new() -> RSsystem<'a> {
 	RSsystem {
-	    delta: RSenvironment::new(),
+	    delta: Rc::new(RSenvironment::new()),
 	    available_entities: RSset::new(),
 	    context_process: RSprocess::Nill,
-	    reaction_rules: vec![],
+	    reaction_rules: Rc::new(vec![]),
 	}
     }
 
-    pub fn from(delta: RSenvironment<'a>,
+    pub fn from(delta: Rc<RSenvironment<'a>>,
 		available_entities: RSset<'a>,
 		context_process: RSprocess<'a>,
-		reaction_rules: Vec<RSreaction<'a>>) -> RSsystem<'a> {
-	RSsystem { delta, available_entities, context_process, reaction_rules }
+		reaction_rules: Rc<Vec<RSreaction<'a>>>) -> RSsystem<'a> {
+	RSsystem { delta: Rc::clone(&delta),
+		   available_entities,
+		   context_process,
+		   reaction_rules: Rc::clone(&reaction_rules) }
     }
 
-    pub fn get_delta(&self) -> &RSenvironment<'a> {
+    pub fn get_delta(&self) -> &Rc<RSenvironment<'a>> {
 	&self.delta
     }
 
@@ -302,7 +305,7 @@ impl<'a> RSsystem<'a> {
 	&self.context_process
     }
 
-    pub fn get_reaction_rules(&self) -> &Vec<RSreaction<'a>> {
+    pub fn get_reaction_rules(&self) -> &Rc<Vec<RSreaction<'a>>> {
 	&self.reaction_rules
     }
 }
diff --git a/src/rsprocess/support_structures.rs b/src/rsprocess/support_structures.rs
index 670a82f..246c43d 100644
--- a/src/rsprocess/support_structures.rs
+++ b/src/rsprocess/support_structures.rs
@@ -65,10 +65,10 @@ impl<'a> Iterator for TransitionsIterator<'a> {
 				  ireactants,
 				  products.clone()
 	);
-	let new_system = RSsystem::from(self.system.get_delta().clone(),
+	let new_system = RSsystem::from(Rc::clone(self.system.get_delta()),
 					products,
 					(*k).clone(),
-					self.system.get_reaction_rules().clone()
+					Rc::clone(self.system.get_reaction_rules())
 	);
 	Some((label, new_system))
     }