diff --git a/src/util.rs b/src/util.rs
index 92f1810b..9badffc1 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -21,7 +21,7 @@ pub(crate) fn create_var(mut id: usize) -> String {
 ///
 /// Returns None when the provided string is not an output of
 /// `create_var`.
-pub fn var_to_num(s: &str) -> Option<usize> {
+pub(crate) fn var_to_num(s: &str) -> Option<usize> {
   let mut n = 0usize;
   for i in s.chars() {
     let i = (i as u32).checked_sub('a' as u32)? as usize;
@@ -53,6 +53,7 @@ fn test_create_var() {
   assert_eq!(create_var(1352), "aza");
   assert_eq!(create_var(1378), "baa");
 }
+
 #[test]
 fn test_var_to_num() {
   for i in [0, 1, 2, 3, 10, 26, 27, 30, 50, 70] {
@@ -178,9 +179,7 @@ impl Tree {
       Tree::Op1 { rgt, .. } => {
         rgt.ensure_no_conflicts(fresh);
       }
-      Tree::Era => (),
-      Tree::Num { .. } => (),
-      Tree::Ref { .. } => (),
+      Tree::Era | Tree::Num { .. } | Tree::Ref { .. } => {},
     }
   }
 }
@@ -198,8 +197,7 @@ impl Net {
   /// The result is equivalent a λ-calculus application. Thus,
   /// if the net is a λ-calculus term, then this function will
   /// apply an argument to it.
-  #[allow(dead_code)] // used in tests
-  pub(crate) fn with_argument(&mut self, arg: Tree) {
+  pub fn apply_tree(&mut self, arg: Tree) {
     let mut fresh = 0usize;
     self.ensure_no_conflicts(&mut fresh);
     arg.ensure_no_conflicts(&mut fresh);
diff --git a/tests/api.rs b/tests/api.rs
index 53c5fefc..e80871ba 100644
--- a/tests/api.rs
+++ b/tests/api.rs
@@ -7,7 +7,7 @@ use hvmc::{
 use insta::assert_display_snapshot;
 
 #[test]
-fn test_with_argument() {
+fn test_apply_tree() {
   use hvmc::run;
   fn eval_with_args(fun: &str, args: &[&str]) -> Net {
     let area = run::Net::<run::Strict>::init_heap(1 << 10);
@@ -15,7 +15,7 @@ fn test_with_argument() {
     let mut fun: Net = fun.parse().unwrap();
     for arg in args {
       let arg: Tree = arg.parse().unwrap();
-      fun.with_argument(arg)
+      fun.apply_tree(arg)
     }
     // TODO: When feature/sc-472/argument-passing, use encode_net instead.
     let mut book = Book::default();
diff --git a/tests/lists.rs b/tests/lists.rs
index 523ba5a4..6e36b594 100644
--- a/tests/lists.rs
+++ b/tests/lists.rs
@@ -8,9 +8,9 @@ fn list_got(index: u32) -> Book {
   let mut book = parse_core(&code);
   println!("{:#?}", book.keys().collect::<Vec<_>>());
   let def = book.get_mut("GenGotIndex").unwrap();
-  def.with_argument(hvmc::ast::Tree::Ref { nam: format!("S{index}") });
+  def.apply_tree(hvmc::ast::Tree::Ref { nam: format!("S{index}") });
   let def = book.get_mut("main").unwrap();
-  def.with_argument(hvmc::ast::Tree::Ref { nam: format!("GenGotIndex") });
+  def.apply_tree(hvmc::ast::Tree::Ref { nam: format!("GenGotIndex") });
   book
 }
 
@@ -18,11 +18,11 @@ fn list_put(index: u32, value: u32) -> Book {
   let code = load_file("list_put_got.hvmc");
   let mut book = parse_core(&code);
   let def = book.get_mut("GenPutIndexValue").unwrap();
-  def.with_argument(hvmc::ast::Tree::Ref { nam: format!("S{index}") });
-  def.with_argument(hvmc::ast::Tree::Ref { nam: format!("S{value}") });
+  def.apply_tree(hvmc::ast::Tree::Ref { nam: format!("S{index}") });
+  def.apply_tree(hvmc::ast::Tree::Ref { nam: format!("S{value}") });
   println!("{:?}", def);
   let def = book.get_mut("main").unwrap();
-  def.with_argument(hvmc::ast::Tree::Ref { nam: format!("GenPutIndexValue") });
+  def.apply_tree(hvmc::ast::Tree::Ref { nam: format!("GenPutIndexValue") });
   book
 }