diff --git a/nested/src/core/context.rs b/nested/src/core/context.rs
index 47d85d5..0765d95 100644
--- a/nested/src/core/context.rs
+++ b/nested/src/core/context.rs
@@ -5,128 +5,411 @@ use {
         any::Any
     },
     crate::{
-        bimap::Bimap,
-        core::type_term::{TypeID, TypeTerm}
+        core::{
+            type_term::{
+                TypeID,
+                TypeTerm,
+                TypeDict
+            },
+            View,
+            OuterViewPort,
+            AnyOuterViewPort
+        }
     }
 };
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
 
-pub enum ReprTree {
-    Leaf(Arc<dyn Any + Send + Sync>),
-    Branch(HashMap<TypeTerm, Arc<RwLock<ReprTree>>>)
+#[derive(Clone)]
+pub struct ReprTree {
+    port: Option<AnyOuterViewPort>,
+    branches: HashMap<TypeTerm, Arc<RwLock<ReprTree>>>
+}
+
+impl ReprTree {
+    pub fn new() -> Self {
+        ReprTree {
+            port: None,
+            branches: HashMap::new()
+        }
+    }
+
+    pub fn new_leaf(
+        port: AnyOuterViewPort
+    ) -> Arc<RwLock<Self>> {
+        let mut tree = ReprTree::new();
+        tree.insert_leaf(vec![].into_iter(), port);
+        Arc::new(RwLock::new(tree))
+    }
+
+    pub fn insert_branch(
+        &mut self,
+        type_tag: TypeTerm,
+        repr: Arc<RwLock<ReprTree>>
+    ) {
+        self.branches.insert(type_tag, repr);
+    }
+
+    pub fn insert_leaf(
+        &mut self,
+        mut type_ladder: impl Iterator<Item = TypeTerm>,
+        port: AnyOuterViewPort
+    ) {
+        if let Some(type_term) = type_ladder.next() {
+            if let Some(next_repr) = self.branches.get(&type_term) {
+                next_repr.write().unwrap().insert_leaf(type_ladder, port);
+            } else {
+                let mut next_repr = ReprTree::new();
+                next_repr.insert_leaf(type_ladder, port);
+                self.insert_branch(type_term, Arc::new(RwLock::new(next_repr)));
+            }
+        } else {
+            self.port = Some(port);
+        }
+    }
 }
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
 
 #[derive(Clone)]
 pub struct Object {
-    type_tag: TypeTerm,
-    repr: Arc<RwLock<ReprTree>>
+    pub type_tag: TypeTerm,
+    pub repr: Arc<RwLock<ReprTree>>
 }
 
 impl Object {
-    fn downcast(&self, repr_type: TypeTerm) -> Option<Object> {
-        match &*self.repr.read().unwrap() {
-            ReprTree::Leaf(data) =>
-                if self.type_tag == repr_type {
-                    Some(self.clone())
-                } else {
-                    None
-                },
-            ReprTree::Branch(reprs) =>
-                Some(Object{
-                    type_tag: repr_type.clone(),
-                    repr: reprs.get(&repr_type)?.clone()
-                })
+    pub fn get_port<V: View + ?Sized + 'static>(&self) -> Option<OuterViewPort<V>> {
+        Some(self.repr.read().unwrap().port.clone()?.downcast::<V>().unwrap())
+    }
+
+    pub fn downcast(&self, dst_type: TypeTerm) -> Option<Object> {
+        if let Some(repr) = self.repr.read().unwrap().branches.get(&dst_type) {
+            Some(Object {
+                type_tag: dst_type,
+                repr: repr.clone()
+            })
+        } else {
+            None
         }
     }
 
-    fn downcast_chain<'a>(
+    fn downcast_ladder(
         &self,
-        repr_chain: impl Iterator<Item = &'a TypeTerm>
+        repr_ladder: impl Iterator<Item = TypeTerm>
     ) -> Option<Object> {
-        repr_chain.fold(
+        repr_ladder.fold(
             Some(self.clone()),
             |s, t| s?.downcast(t.clone())
         )
     }
 
-    fn get_data<T: Any + Send + Sync>(&self) -> Option<Arc<T>> {
-        match &*self.repr.read().unwrap() {
-            ReprTree::Leaf(data) => Arc::downcast::<T>(data.clone()).ok(),
-            _ => None
+    pub fn add_iso_repr(
+        &self,
+        type_ladder: impl Iterator<Item = TypeTerm>,
+        morphism_constructors: &HashMap<MorphismType, Box<dyn Fn(Object) -> Object>>
+    ) {
+        let mut cur_repr = self.repr.clone();
+
+        for dst_type in type_ladder {
+            if let Some(next_repr) = self.repr.read().unwrap().branches.get(&dst_type) {
+                // go deeper
+                cur_repr = next_repr.clone();
+            } else {
+                // search for morphism constructor and insert new repr
+                let mut obj = None;
+
+                for src_type in cur_repr.read().unwrap().branches.keys() {
+                    if let Some(ctor) = morphism_constructors.get(
+                        &MorphismType {
+                            mode: MorphismMode::Iso,
+                            src_type: src_type.clone(),
+                            dst_type: dst_type.clone()
+                        }
+                    ) {
+                        let new_obj = ctor(
+                            Object {
+                                type_tag: src_type.clone(),
+                                repr: cur_repr.read().unwrap()
+                                    .branches
+                                    .get(&src_type).unwrap().clone()
+                            }
+                        );
+
+                        assert!(new_obj.type_tag == dst_type);
+
+                        obj = Some(new_obj);
+                        break;
+                    }
+                }
+
+                if let Some(obj) = obj {
+                    cur_repr.write().unwrap().insert_branch(obj.type_tag, obj.repr);
+                } else {
+                    panic!("could not find matching isomorphism!");
+                }
+            }
         }
-    }    
+    }
+
+    pub fn add_mono_repr<'a>(
+        &self,
+        type_ladder: impl Iterator<Item = TypeTerm>,
+        morphism_constructors: &HashMap<MorphismType, Box<dyn Fn(Object) -> Object>>
+    ) {
+        let mut cur_type = self.type_tag.clone();
+        let mut cur_repr = self.repr.clone();
+
+        for dst_type in type_ladder {
+            if let Some(next_repr) = self.repr.read().unwrap().branches.get(&dst_type) {
+                // go deeper
+                cur_type = dst_type;
+                cur_repr = next_repr.clone();
+            } else {
+                if let Some(constructor) = morphism_constructors.get(
+                    &MorphismType {
+                        mode: MorphismMode::Mono,
+                        src_type: cur_type.clone(),
+                        dst_type: dst_type.clone()
+                    }
+                ) {
+                    let new_obj = constructor(
+                        Object {
+                            type_tag: cur_type.clone(),
+                            repr: cur_repr.read().unwrap()
+                                .branches
+                                .get(&cur_type).unwrap().clone()
+                        }
+                    );
+
+                    assert!(new_obj.type_tag == dst_type);
+                    cur_repr.write().unwrap().insert_branch(new_obj.type_tag.clone(), new_obj.repr.clone());
+
+                    cur_type = new_obj.type_tag;
+                    cur_repr = new_obj.repr;
+                }
+            }
+        }
+    }
+
+    // replace with higher-level type in which self is a repr branch
+    pub fn epi_cast<'a>(
+        &self,
+        type_ladder: impl Iterator<Item = TypeTerm>,
+        morphism_constructors: &HashMap<MorphismType, Box<dyn Fn(Object) -> Object>>
+    ) {
+        // todo        
+    }
 }
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
 
-pub struct TypeDict {
-    typenames: Bimap::<String, u64>,
-    type_id_counter: u64
+#[derive(Clone, Copy, Hash, PartialEq, Eq)]
+pub enum MorphismMode {
+    /// Isomorphism
+    /// e.g. `( PositionalInteger 10 BigEndian ) <~> ( PositionalInteger 16 LittleEndian )`
+    Iso,
+
+    /// Monomorphism, i.e. injective functions,
+    /// upcast-view, downcast-control, semantic gain
+    /// e.g. `( Sequence ( Digit 16 ) ) ~> ( PositionalInteger 16 LittleEndian )`
+    Mono,
+
+    /// Epimorphsim, i.e. surjective functions,
+    /// upcast-control, downcast-view, possible loss of entropy
+    /// e.g. `( Ascii ) ~> ( Digit 16 )`
+    Epi,
+
+    /// Any other function
+    Any
 }
 
-impl TypeDict {
-    pub fn new() -> Self {
-        TypeDict {
-            typenames: Bimap::new(),
-            type_id_counter: 0
-        }
-    }
-
-    pub fn add_typename(&mut self, tn: String) {
-        self.typenames.insert(tn, self.type_id_counter);
-        self.type_id_counter += 1;
-    }
-
-    pub fn type_term_from_str(&self, typename: &str) -> Option<TypeTerm> {
-        TypeTerm::from_str(typename, &self.typenames.mλ)
-    }
-
-    pub fn type_term_to_str(&self, term: &TypeTerm) -> String {
-        term.to_str(&self.typenames.my)
-    }
+#[derive(Clone, Hash, PartialEq, Eq)]
+pub struct MorphismType {
+    pub mode: MorphismMode,
+    pub src_type: TypeTerm,
+    pub dst_type: TypeTerm
 }
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
 
 pub struct Context {
     type_dict: TypeDict,
-
-    // map type_id -> constructor
-    constructors: HashMap<u64, Box<Fn() -> Arc<dyn Any + Send + Sync>>>,
-
-    objects: HashMap<String, Object>
+    default_constructors: HashMap<TypeTerm, Box<dyn Fn() -> Object + Send + Sync>>,
+    morphism_constructors: HashMap<MorphismType, Box<dyn Fn(Object) -> Object + Send + Sync>>,
+    objects: HashMap<String, Object>,
+    parent: Option<Arc<RwLock<Context>>>
 }
 
 impl Context {
+    pub fn with_parent(parent: Option<Arc<RwLock<Context>>>) -> Self {
+        Context {
+            type_dict: TypeDict::new(),
+            default_constructors: HashMap::new(),
+            morphism_constructors: HashMap::new(),
+            objects: HashMap::new(),
+            parent
+        }
+    }
+
+    pub fn new() -> Self {
+        Context::with_parent(None)
+    }
+
+    pub fn add_typename(&mut self, tn: String) {
+        self.type_dict.add_typename(tn);
+    }
+
+    pub fn type_term_from_str(&self, tn: &str) -> Option<TypeTerm> {
+        self.type_dict.type_term_from_str(&tn)
+    }
+
+    pub fn add_morphism(
+        &mut self,
+        morph_type: MorphismType,
+        morph_fn: Box<dyn Fn(Object) -> Object + Send + Sync>
+    ) {
+        self.morphism_constructors.insert(morph_type, morph_fn);
+    }
+
+    /// adds an object without any representations
     pub fn add_obj(
         &mut self,
         name: String,
         typename: &str
     ) {
+        let type_tag = self.type_dict.type_term_from_str(typename).unwrap();
+
         self.objects.insert(
             name,
-            Object {
-                type_tag: self.type_dict.type_term_from_str(typename).unwrap(),
-                repr: Arc::new(RwLock::new(ReprTree::Branch(HashMap::new())))
+            if let Some(ctor) = self.default_constructors.get(&type_tag) {
+                ctor()
+            } else {
+                Object {
+                    type_tag,
+                    repr: Arc::new(RwLock::new(ReprTree::new()))
+                }
+
             }
         );
     }
 
-    pub fn add_repr(&mut self, name: &String, typename: &str, repr: Arc<RwLock<ReprTree>>) {
-        match &mut *self.objects.get_mut(name).unwrap().repr.write().unwrap() {
-            ReprTree::Leaf(_) => {/*error*/},
-            ReprTree::Branch(repr_map) => {
-                repr_map.insert(self.type_dict.type_term_from_str(typename).unwrap(), repr.clone());
-            }
+    pub fn get_obj(
+        &self,
+        name: &String
+    ) -> Option<Object> {
+        if let Some(obj) = self.objects.get(name) {
+            Some(obj.clone())
+        } else if let Some(parent) = self.parent.as_ref() {
+            parent.read().unwrap().get_obj(name)
+        } else {
+            None
+        }
+    }
+ 
+    pub fn get_obj_port<
+        'a,
+        V: View + ?Sized + 'static
+    >(
+        &self,
+        name: &str,
+        type_ladder: impl Iterator<Item = &'a str>
+    ) -> Option<OuterViewPort<V>> {
+        self.get_obj(&name.into())?
+            .downcast_ladder(
+                type_ladder.map(|tn| self.type_dict.type_term_from_str(tn).unwrap())
+            )?
+            .get_port()
+    }
+
+    pub fn insert_repr<'a>(
+        &mut self,
+        name: &str,
+        type_ladder: impl Iterator<Item = &'a str>,
+        port: AnyOuterViewPort
+    ) {
+        self.get_obj(&name.to_string()).unwrap()
+            .repr.write().unwrap()
+            .insert_leaf(
+                type_ladder.map(|tn| self.type_dict.type_term_from_str(tn).unwrap()),
+                port
+            );
+    }
+
+    pub fn epi_cast(
+        &mut self,
+        name: &str,
+        typename: &str
+    ) {
+        let dst_type = self.type_dict.type_term_from_str(typename).unwrap();
+        let mut old_obj = self.objects.get(&name.to_string()).unwrap().clone();
+        let mut new_obj =
+            if let Some(ctor) = self.morphism_constructors.get(
+                &MorphismType {
+                    mode: MorphismMode::Epi,
+                    src_type: old_obj.type_tag.clone(),
+                    dst_type: dst_type.clone()
+                }
+            ) {
+                ctor(old_obj.clone())
+            } else {
+                Object {
+                    type_tag: dst_type,
+                    repr: Arc::new(RwLock::new(ReprTree::new()))
+                }
+            };
+
+        new_obj.repr.write().unwrap().insert_branch(
+            old_obj.type_tag,
+            old_obj.repr
+        );
+
+        self.objects.insert(name.to_string(), new_obj);
+    }
+
+    pub fn mono_view<'a, V: View + ?Sized + 'static>(
+        &mut self,
+        name: &str,
+        type_ladder: impl Iterator<Item = &'a str>
+    ) -> Option<OuterViewPort<V>> {
+        if let Some(p) = self.get_obj_port(name, type_ladder) {
+            Some(p)
+        } else {
+            // todo : add repr with morphism constructor (if one exists)
+            /*
+            if let Some(ctor) = self.morphism_constructors.get(
+                &MorphismType {
+                    mode: MorphismMode::Mono,
+                    src_type: old_obj.type_tag.clone(),
+                    dst_type: 
+                }
+            )
+            */
+            None
         }
     }
 
-    pub fn get_obj(&self, name: &String) -> Option<Object> {
-        self.objects.get(name).cloned()
+/*
+    pub fn _default_repr<'a>(
+        &mut self,
+        name: &String,
+        type_ladder: impl Iterator<Item = &'a str>
+    ) -> AnyOuterViewPort {
+        for (i, type_term) in type_ladder.rev().enumerate() {
+            match i {
+                0 => {
+                    if let Some(constructor) = self.default_constructors.get(&type_term) {
+                        self.add_repr()
+                    } else {
+                        panic!("cannot find matching default constructor!");
+                    }
+                }
+                _n => {
+                    
+                }
+            }
+        }
     }
+     */
 }
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
diff --git a/nested/src/core/mod.rs b/nested/src/core/mod.rs
index a0cb989..7a4d12b 100644
--- a/nested/src/core/mod.rs
+++ b/nested/src/core/mod.rs
@@ -25,17 +25,22 @@ pub use {
     port::{
         ViewPort,
         InnerViewPort,
-        OuterViewPort
+        OuterViewPort,
+        AnyViewPort,
+        AnyOuterViewPort,
+        AnyInnerViewPort,
     },
     type_term::{
         TypeID,
-        TypeTerm
+        TypeTerm,
+        TypeDict,
     },
     context::{
         ReprTree,
-        TypeDict,
+        Object,
         Context,
-        Object
+        MorphismMode,
+        MorphismType
     }
 };
 
diff --git a/nested/src/core/type_term.rs b/nested/src/core/type_term.rs
index 044413a..784791d 100644
--- a/nested/src/core/type_term.rs
+++ b/nested/src/core/type_term.rs
@@ -1,9 +1,14 @@
-use std::{
-    sync::Arc,
-    any::Any,
-    ops::Deref,
-    collections::HashMap,
-    iter::Peekable
+use {
+    std::{
+        sync::Arc,
+        any::Any,
+        ops::Deref,
+        collections::HashMap,
+        iter::Peekable
+    },
+    crate::{
+        bimap::Bimap,
+    }
 };
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
@@ -131,3 +136,32 @@ impl TypeTerm {
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
 
+pub struct TypeDict {
+    typenames: Bimap::<String, u64>,
+    type_id_counter: u64
+}
+
+impl TypeDict {
+    pub fn new() -> Self {
+        TypeDict {
+            typenames: Bimap::new(),
+            type_id_counter: 0
+        }
+    }
+
+    pub fn add_typename(&mut self, tn: String) {
+        self.typenames.insert(tn, self.type_id_counter);
+        self.type_id_counter += 1;
+    }
+
+    pub fn type_term_from_str(&self, typename: &str) -> Option<TypeTerm> {
+        TypeTerm::from_str(typename, &self.typenames.mλ)
+    }
+
+    pub fn type_term_to_str(&self, term: &TypeTerm) -> String {
+        term.to_str(&self.typenames.my)
+    }
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+