diff --git a/src/flow/binary.rs b/src/flow/binary.rs
index 9c8918e..2c7378c 100644
--- a/src/flow/binary.rs
+++ b/src/flow/binary.rs
@@ -51,24 +51,23 @@ pub trait BinaryTreesMutable<'a>: BinaryTrees<'a> {
         <Self::T as Monad>::bind(self.clone().join_key(tl, key, tr), move |n| self.tree_of(n))
     }
 
-    fn join(&self, tl: Self::Tree, tr: Self::Tree) -> BTWrap<'a, Self, Self::Tree> {
+    fn join(self, tl: Self::Tree, tr: Self::Tree) -> BTWrap<'a, Self, Self::Tree> {
         let Some(rl) = self.refer(&tl) else {
             return <Self::T as Pure>::pure(tr)
         };
         let Some(rr) = self.refer(&tr) else {
             return <Self::T as Pure>::pure(tl)
         };
-        let ctx = self.clone();
         Self::T::bind2(self.resolve(&rl), self.resolve(&rr), move |nl, nr| {
-            let (tll, tlr, kl) = ctx.split(&nl);
-            let (trl, trr, kr) = ctx.split(&nr);
-            let ft = ctx.join(tlr, trl);
+            let (tll, tlr, kl) = self.split(&nl);
+            let (trl, trr, kr) = self.split(&nr);
+            let ft = self.clone().join(tlr, trl);
             let ft = {
-                let ctx = ctx.clone();
+                let ctx = self.clone();
                 <Self::T as Monad>::bind(ft, move |t| ctx.join_key_tree(tll, kl, t))
             };
             let ft = {
-                let ctx = ctx.clone();
+                let ctx = self.clone();
                 <Self::T as Monad>::bind(ft, move |t| ctx.join_key_tree(t, kr, trr))
             };
             ft
@@ -124,6 +123,12 @@ pub trait BinaryTreesMutable<'a>: BinaryTrees<'a> {
     fn add_tree(self, tree: Self::Tree, key: KeyRc<'a, Self>) -> BTWrap<'a, Self, Self::Tree> {
         <Self::T as Monad>::bind(self.clone().add(tree, key), move |n| self.tree_of(n))
     }
+
+    fn remove(self, tree: Self::Tree, key: KeyRc<'a, Self>) -> BTWrap<'a, Self, Self::Tree> {
+        <Self::T as Monad>::bind(self.clone().split_key(tree, key.clone()), |(tl, tr)| {
+            self.join(tl, tr)
+        })
+    }
 }
 
 pub trait BinaryTreesAvl<'a>: BinaryTrees<'a> {