diff --git a/lib-nested-core/src/repr_tree/context.rs b/lib-nested-core/src/repr_tree/context.rs
index e7cad72..37f16ae 100644
--- a/lib-nested-core/src/repr_tree/context.rs
+++ b/lib-nested-core/src/repr_tree/context.rs
@@ -1,7 +1,7 @@
 use {
     crate::{
         edit_tree::EditTree,
-        repr_tree::{GenericReprTreeMorphism, ReprTree, ReprTreeExt},
+        repr_tree::{GenericReprTreeMorphism, ReprTree, ReprTreeExt, ReprTreeArc},
     },
     laddertypes::{
         parser::ParseLadderType, sugar::SugaredTypeTerm, unparser::UnparseLadderType,
@@ -152,7 +152,7 @@ impl Context {
         }
     }
 
-    pub fn make_repr(ctx: &Arc<RwLock<Self>>, t: &TypeTerm) -> Arc<RwLock<ReprTree>> {
+    pub fn make_repr(ctx: &Arc<RwLock<Self>>, t: &TypeTerm) -> ReprTreeArc {
         let rt = Arc::new(RwLock::new(ReprTree::new( TypeTerm::unit() )));
         ctx.read().unwrap().apply_morphism( &rt, &MorphismType{ src_type: TypeTerm::unit(), dst_type: t.clone() } );
         rt
@@ -242,7 +242,7 @@ impl Context {
 */
     }
 
-    pub fn get_obj(&self, name: &String) -> Option< Arc<RwLock<ReprTree>> > {
+    pub fn get_obj(&self, name: &String) -> Option< ReprTreeArc > {
         if let Some(obj) = self.nodes.get(name) {
             Some(obj.clone())
         } else if let Some(parent) = self.parent.as_ref() {
diff --git a/lib-nested-core/src/repr_tree/mod.rs b/lib-nested-core/src/repr_tree/mod.rs
index 8af48f8..e77774f 100644
--- a/lib-nested-core/src/repr_tree/mod.rs
+++ b/lib-nested-core/src/repr_tree/mod.rs
@@ -9,7 +9,7 @@ mod tests;
 pub use {
     context::{Context},
     leaf::ReprLeaf,
-    node::ReprTree,
+    node::{ReprTree, ReprTreeArc},
     morphism::{GenericReprTreeMorphism}
 };
 
@@ -42,7 +42,7 @@ pub trait ReprTreeExt {
     fn insert_leaf(&mut self, type_ladder: impl Into<TypeTerm>, leaf: ReprLeaf);
     fn insert_branch(&mut self, repr: Arc<RwLock<ReprTree>>);
     fn create_branch(&mut self, rung: impl Into<TypeTerm>);
-    fn descend(&self, target_type: impl Into<TypeTerm>) -> Option<Arc<RwLock<ReprTree>>>;
+    fn descend(&self, target_type: impl Into<TypeTerm>) -> Option< ReprTreeArc >;
 
     fn attach_leaf_to<V: View + ?Sized + 'static>(&self, t: impl Into<TypeTerm>, v: OuterViewPort<V>) where V::Msg: Clone;
     fn get_port<V: View + ?Sized + 'static>(&self) -> Option<OuterViewPort<V>> where V::Msg: Clone;
@@ -100,7 +100,7 @@ impl ReprTreeExt for Arc<RwLock<ReprTree>> {
         self.write().unwrap().attach_leaf_to::<V>(type_ladder.into().get_lnf_vec().into_iter(), v)
     }
 
-    fn descend(&self, target_type: impl Into<TypeTerm>) -> Option<Arc<RwLock<ReprTree>>> {
+    fn descend(&self, target_type: impl Into<TypeTerm>) -> Option< ReprTreeArc > {
         ReprTree::descend( self, target_type )
     }
 
diff --git a/lib-nested-core/src/repr_tree/node.rs b/lib-nested-core/src/repr_tree/node.rs
index 837092e..bef682b 100644
--- a/lib-nested-core/src/repr_tree/node.rs
+++ b/lib-nested-core/src/repr_tree/node.rs
@@ -28,10 +28,12 @@ use {
 pub struct ReprTree {
     halo: TypeTerm,
     type_tag: TypeTerm,
-    branches: HashMap<TypeTerm, Arc<RwLock<ReprTree>>>,
+    branches: HashMap<TypeTerm, ReprTreeArc>,
     leaf: Option< ReprLeaf >
 }
 
+pub type ReprTreeArc = Arc<RwLock<ReprTree>>;
+
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
 
 impl std::fmt::Debug for ReprTree {
@@ -67,7 +69,7 @@ impl ReprTree {
         }
     }
 
-    pub fn new_arc(type_tag: impl Into<TypeTerm>) -> Arc<RwLock<Self>> {
+    pub fn new_arc(type_tag: impl Into<TypeTerm>) -> ReprTreeArc {
         Arc::new(RwLock::new(Self::new(type_tag)))
     }
 
@@ -106,7 +108,7 @@ impl ReprTree {
         leaf_types
     }
 
-    pub fn insert_branch(&mut self, repr: Arc<RwLock<ReprTree>>) {
+    pub fn insert_branch(&mut self, repr: ReprTreeArc) {
         let branch_type = repr.read().unwrap().get_type().clone();
 
         assert!(branch_type.is_flat());
@@ -119,14 +121,14 @@ impl ReprTree {
         self.branches.insert(branch_type, repr.clone());
     }
 
-    pub fn from_char(ctx: &Arc<RwLock<Context>>, c: char ) -> Arc<RwLock<Self>> {
+    pub fn from_char(ctx: &Arc<RwLock<Context>>, c: char ) -> ReprTreeArc {
         ReprTree::from_singleton_buffer(
             Context::parse(ctx, "Char"),
             SingletonBuffer::new(c)
         )
     }
 
-    pub fn from_view<V>( type_tag: impl Into<TypeTerm>, view: OuterViewPort<V> ) -> Arc<RwLock<Self>>
+    pub fn from_view<V>( type_tag: impl Into<TypeTerm>, view: OuterViewPort<V> ) -> ReprTreeArc
     where V: View + ?Sized + 'static,
         V::Msg: Clone
     {
@@ -135,7 +137,7 @@ impl ReprTree {
         Arc::new(RwLock::new(rt))
     }
 
-    pub fn from_singleton_buffer<T>( type_tag: impl Into<TypeTerm>, buf: SingletonBuffer<T> ) -> Arc<RwLock<Self>>
+    pub fn from_singleton_buffer<T>( type_tag: impl Into<TypeTerm>, buf: SingletonBuffer<T> ) -> ReprTreeArc
     where T: Clone + Send + Sync + 'static
     {
         let mut rt = ReprTree::new(type_tag);
@@ -146,7 +148,7 @@ impl ReprTree {
     pub fn from_str(
         type_tag: impl Into<TypeTerm>,
         val: &str
-    ) -> Arc<RwLock<Self>> {
+    ) -> ReprTreeArc {
         let mut lnf = type_tag.into().get_lnf_vec();
 
         let mut rt = ReprTree::from_vec_buffer(
@@ -163,7 +165,7 @@ impl ReprTree {
         rt
     }
 
-    pub fn from_vec_buffer<T>( type_tag: impl Into<TypeTerm>, buf: VecBuffer<T> ) -> Arc<RwLock<Self>>
+    pub fn from_vec_buffer<T>( type_tag: impl Into<TypeTerm>, buf: VecBuffer<T> ) -> ReprTreeArc
     where T: Clone + Send + Sync + 'static
     {
         let mut rt = ReprTree::new(type_tag);
@@ -340,13 +342,13 @@ impl ReprTree {
 
     //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
 
-    pub fn descend_one(&self, dst_type: impl Into<TypeTerm>) -> Option<Arc<RwLock<ReprTree>>> {
+    pub fn descend_one(&self, dst_type: impl Into<TypeTerm>) -> Option< ReprTreeArc > {
         let dst_type = dst_type.into();
         assert!( dst_type.is_flat() );
         self.branches.get(&dst_type).cloned()
     }
 
-    pub fn descend_ladder(rt: &Arc<RwLock<Self>>, mut repr_ladder: impl Iterator<Item = TypeTerm>) -> Option<Arc<RwLock<ReprTree>>> {
+    pub fn descend_ladder(rt: &Arc<RwLock<Self>>, mut repr_ladder: impl Iterator<Item = TypeTerm>) -> Option< ReprTreeArc > {
         if let Some(first) = repr_ladder.next() {
             let rt = rt.read().unwrap();
             repr_ladder.fold(
@@ -357,7 +359,7 @@ impl ReprTree {
         }
     }
 
-    pub fn descend(rt: &Arc<RwLock<Self>>, dst_type: impl Into<TypeTerm>) -> Option<Arc<RwLock<ReprTree>>> {
+    pub fn descend(rt: &Arc<RwLock<Self>>, dst_type: impl Into<TypeTerm>) -> Option< ReprTreeArc > {
         let mut lnf = dst_type.into().get_lnf_vec();
         if lnf.len() > 0 {
             if lnf[0] == rt.get_type() {