diff --git a/Cargo.toml b/Cargo.toml
index 7ac97b9..c388d58 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,7 +2,7 @@
 name = "reactionsystems"
 version = "0.1.0"
 edition = "2024"
-exclude = ["*.system", "*.experiment", "/testing/", "*.serial"]
+exclude = ["*.system", "*.experiment", "/testing/", "*.serial", "*.dot", "*.trace", "*.svg"]
 
 [build-dependencies]
 lalrpop = "0.22"
diff --git a/src/rsprocess/set.rs b/src/rsprocess/set.rs
index a2be930..7f08302 100644
--- a/src/rsprocess/set.rs
+++ b/src/rsprocess/set.rs
@@ -80,9 +80,7 @@ impl BasicSet for Set {
 
     // returns the new set a \cup b
     fn union(&self, other: &Self) -> Self {
-	let mut ret: Self = other.clone();
-	ret.identifiers.extend(self.identifiers.iter());
-	ret
+	self.iter().chain(other.iter()).cloned().collect::<Vec<_>>().into()
     }
 
     fn push(&mut self, other: &Self) {
@@ -355,9 +353,8 @@ impl BasicSet for PositiveSet {
     /// ☞ The operation cannot fail, so we prefer self elements to other,
     /// but if the reaction system is consistent there wont be any problem.
     fn union(&self, other: &Self) -> Self {
-	let mut ret: Self = other.clone();
-	ret.identifiers.extend(self.identifiers.iter());
-	ret
+	self.iter().chain(other.iter()).map(|(a, b)| (*a, *b))
+	    .collect::<Vec<_>>().into()
     }
 
     fn push(&mut self, other: &Self) {