diff --git a/assert/src/tests.rs b/assert/src/tests.rs
index f2a72d9..f7cf3f6 100644
--- a/assert/src/tests.rs
+++ b/assert/src/tests.rs
@@ -1274,7 +1274,7 @@ fn for_8() {
 
 #[test]
 fn nodes() {
-    use std::rc::Rc;
+    use std::sync::Arc;
 
     use environment::Environment;
     use label::Label;
@@ -1321,10 +1321,10 @@ fn nodes() {
     let mut graph = petgraph::Graph::new();
     let node_1 = graph.add_node(System::default());
     let node_2 = graph.add_node(System::from(
-        Rc::new(Environment::default()),
+        Arc::new(Environment::default()),
         Set::from([2]),
         Process::Nill,
-        Rc::new(vec![]),
+        Arc::new(vec![]),
     ));
     let edge = graph.add_edge(node_1, node_2, Label::default());
 
diff --git a/rsprocess/src/process.rs b/rsprocess/src/process.rs
index fa099ba..f926673 100644
--- a/rsprocess/src/process.rs
+++ b/rsprocess/src/process.rs
@@ -32,8 +32,9 @@ where
 
 // -----------------------------------------------------------------------------
 
-#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize, Default)]
 pub enum Process {
+    #[default]
     Nill,
     RecursiveIdentifier {
         identifier: IdType,
@@ -152,12 +153,6 @@ impl BasicProcess for Process {
     }
 }
 
-impl Default for Process {
-    fn default() -> Self {
-        Self::Nill
-    }
-}
-
 impl PrintableWithTranslator for Process {
     fn print(
         &self,
@@ -247,8 +242,9 @@ impl PrintableWithTranslator for Process {
 
 // -----------------------------------------------------------------------------
 
-#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize, Default)]
 pub enum PositiveProcess {
+    #[default]
     Nill,
     RecursiveIdentifier {
         identifier: IdType,
@@ -365,12 +361,6 @@ impl BasicProcess for PositiveProcess {
     }
 }
 
-impl Default for PositiveProcess {
-    fn default() -> Self {
-        Self::Nill
-    }
-}
-
 impl PrintableWithTranslator for PositiveProcess {
     fn print(
         &self,