diff --git a/nested/src/editors/integer/editor.rs b/nested/src/editors/integer/editor.rs
index d324017..89e9a9c 100644
--- a/nested/src/editors/integer/editor.rs
+++ b/nested/src/editors/integer/editor.rs
@@ -116,7 +116,7 @@ impl DigitEditor {
         TypeTerm::Type {
             id: self.ctx.read().unwrap().get_typeid("Digit").unwrap(),
             args: vec![
-                TypeTerm::Num(self.radix as i64)
+                TypeTerm::Num(self.radix as i64).into()
             ]
         }
     }
@@ -145,7 +145,7 @@ impl PosIntEditor {
             TypeTerm::Type {
                 id: ctx.read().unwrap().get_typeid("Digit").unwrap(),
                 args: vec![
-                    TypeTerm::Num(radix as i64)
+                    TypeTerm::Num(radix as i64).into()
                 ]
             },
             None,
@@ -169,11 +169,11 @@ impl PosIntEditor {
             TypeTerm::Type {
                 id: ctx.read().unwrap().get_typeid("PosInt").unwrap(),
                 args: vec![
-                    TypeTerm::Num(radix as i64),
+                    TypeTerm::Num(radix as i64).into(),
                     TypeTerm::Type {
                         id: ctx.read().unwrap().get_typeid("BigEndian").unwrap(),
                         args: vec![]
-                    }
+                    }.into()
                 ]
             }
         ));
diff --git a/nested/src/editors/list/editor.rs b/nested/src/editors/list/editor.rs
index c96e1e2..0c28269 100644
--- a/nested/src/editors/list/editor.rs
+++ b/nested/src/editors/list/editor.rs
@@ -125,8 +125,8 @@ impl ListEditor {
     pub fn get_seq_type(&self) -> TypeTerm {
         TypeTerm::Type {
             id: self.ctx.read().unwrap().get_typeid("List").unwrap(),
-            args: vec![ self.get_item_type() ]
-        }        
+            args: vec![ self.get_item_type().into() ]
+        }
     }
 
     pub fn get_cursor_port(&self) -> OuterViewPort<dyn SingletonView<Item = ListCursor>> {
diff --git a/nested/src/type_system/context.rs b/nested/src/type_system/context.rs
index 5d5bec1..cf9fd85 100644
--- a/nested/src/type_system/context.rs
+++ b/nested/src/type_system/context.rs
@@ -1,6 +1,6 @@
 use {
     crate::{
-        type_system::{TypeDict, TypeTerm, TypeID, ReprTree},
+        type_system::{TypeDict, TypeTerm, TypeID, ReprTree, TypeLadder},
         tree::NestedNode
     },
     std::{
@@ -11,8 +11,6 @@ use {
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
 
-pub struct TypeLadder(Vec<TypeTerm>);
-
 #[derive(Clone, Copy, Hash, PartialEq, Eq)]
 pub enum MorphismMode {
     /// Isomorphism
@@ -50,12 +48,12 @@ impl From<MorphismType> for MorphismTypePattern {
     fn from(value: MorphismType) -> MorphismTypePattern {
         MorphismTypePattern {
             src_tyid: match value.src_type {
-                Some(TypeTerm::Type { id, args: _ }) => Some(id),
+                Some(TypeTerm::Type { id, args: _ }) => Some(TypeID::Fun(id)),
                 _ => None,
             },
 
             dst_tyid: match value.dst_type {
-                TypeTerm::Type { id, args: _ } => id,
+                TypeTerm::Type { id, args: _ } => TypeID::Fun(id),
                 _ => unreachable!()
             }
         }
@@ -66,7 +64,7 @@ impl From<MorphismType> for MorphismTypePattern {
 
 pub struct Context {
     /// assigns a name to every type
-    type_dict: Arc<RwLock<TypeDict>>,
+    pub type_dict: Arc<RwLock<TypeDict>>,
 
     /// named vertices of the graph
     nodes: HashMap< String, NestedNode >,
@@ -135,7 +133,7 @@ impl Context {
     pub fn is_list_type(&self, t: &TypeTerm) -> bool {
         match t {
             TypeTerm::Type { id, args: _ } => {
-                self.list_types.contains(id)
+                self.list_types.contains(&TypeID::Fun(*id))
             }
             _ => false
         }
@@ -145,6 +143,20 @@ impl Context {
         self.type_dict.read().unwrap().get_typeid(&tn.into())
     }
 
+    pub fn get_fun_typeid(&self, tn: &str) -> Option<u64> {
+        match self.get_typeid(tn) {
+            Some(TypeID::Fun(x)) => Some(x),
+            _ => None
+        }
+    }
+
+    pub fn get_var_typeid(&self, tn: &str) -> Option<u64> {
+        match self.get_typeid(tn) {
+            Some(TypeID::Var(x)) => Some(x),
+            _ => None
+        }
+    }
+
     pub fn type_term_from_str(&self, tn: &str) -> Option<TypeTerm> {
         self.type_dict.read().unwrap().type_term_from_str(&tn)
     }
diff --git a/nested/src/type_system/dict.rs b/nested/src/type_system/dict.rs
new file mode 100644
index 0000000..7ef52f6
--- /dev/null
+++ b/nested/src/type_system/dict.rs
@@ -0,0 +1,71 @@
+use {
+    crate::{
+        utils::Bimap,
+        type_system::{TypeTerm, TypeLadder}
+    }
+};
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+#[derive(Eq, PartialEq, Hash, Clone, Debug)]
+pub enum TypeID {
+    Fun(u64),
+    Var(u64)
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+pub struct TypeDict {
+    typenames: Bimap<String, TypeID>,
+    type_lit_counter: u64,
+    type_var_counter: u64,
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+impl TypeDict {
+    pub fn new() -> Self {
+        TypeDict {
+            typenames: Bimap::new(),
+            type_lit_counter: 0,
+            type_var_counter: 0,
+        }
+    }
+
+    pub fn add_varname(&mut self, tn: String) -> TypeID {
+        let tyid = TypeID::Var(self.type_var_counter);
+        self.type_var_counter += 1;
+        self.typenames.insert(tn, tyid.clone());
+        tyid
+    }
+
+    pub fn add_typename(&mut self, tn: String) -> TypeID {
+        let tyid = TypeID::Fun(self.type_lit_counter);
+        self.type_lit_counter += 1;
+        self.typenames.insert(tn, tyid.clone());
+        tyid
+    }
+
+    pub fn get_typename(&self, tid: &TypeID) -> Option<String> {
+        self.typenames.my.get(tid).cloned()
+    }
+
+    pub fn get_typeid(&self, tn: &String) -> Option<TypeID> {
+        self.typenames.mλ.get(tn).cloned()
+    }
+
+    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)
+    }
+
+    pub fn type_ladder_to_str(&self, ladder: &TypeLadder) -> String {
+        ladder.to_str1(&self.typenames.my)
+    }
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
diff --git a/nested/src/type_system/type_term_editor.rs b/nested/src/type_system/editor.rs
similarity index 100%
rename from nested/src/type_system/type_term_editor.rs
rename to nested/src/type_system/editor.rs
diff --git a/nested/src/type_system/ladder.rs b/nested/src/type_system/ladder.rs
new file mode 100644
index 0000000..d730452
--- /dev/null
+++ b/nested/src/type_system/ladder.rs
@@ -0,0 +1,71 @@
+use {
+    crate::type_system::{TypeTerm, TypeID},
+    std::collections::HashMap
+};
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+#[derive(Clone, Eq, PartialEq, Hash, Debug)]
+pub struct TypeLadder(pub Vec<TypeTerm>);
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
+impl From<Vec<TypeTerm>> for TypeLadder {
+    fn from(l: Vec<TypeTerm>) -> Self {
+        TypeLadder(l)
+    }
+}
+
+impl From<TypeTerm> for TypeLadder {
+    fn from(l: TypeTerm) -> Self {
+        TypeLadder(vec![ l ])
+    }
+}
+
+impl TypeLadder {
+    /// if compatible, returns the number of descents neccesary
+    pub fn is_compatible_with(&self, other: &TypeLadder) -> Option<usize> {
+        if let Some(other_top_type) = other.0.first() {
+            for (i, t) in self.0.iter().enumerate() {
+                if t == other_top_type {
+                    return Some(i);
+                }
+            }
+
+            None
+        } else {
+            None
+        }
+    }
+
+    pub fn is_matching_repr(&self, other: &TypeLadder) -> Result<usize, Option<(usize, usize)>> {
+        if let Some(start) = self.is_compatible_with(other) {
+            for (i, (t1, t2)) in self.0.iter().skip(start).zip(other.0.iter()).enumerate() {
+                if t1 != t2 {
+                    return Err(Some((start, i)));
+                }
+            }
+
+            Ok(start)
+        } else {
+            Err(None)
+        }
+    }
+
+    pub fn to_str1(&self, names: &HashMap<TypeID, String>) -> String {
+        let mut s = String::new();
+        let mut first = true;
+
+        for t in self.0.iter() {
+            if !first {
+                s = s + "~";
+            }
+            first = false;
+            s = s + &t.to_str1(names);
+        }
+        s
+    }
+}
+
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
diff --git a/nested/src/type_system/make_editor.rs b/nested/src/type_system/make_editor.rs
index 9e5b02c..5da6a09 100644
--- a/nested/src/type_system/make_editor.rs
+++ b/nested/src/type_system/make_editor.rs
@@ -75,7 +75,7 @@ pub fn init_editor_ctx(parent: Arc<RwLock<Context>>) -> Arc<RwLock<Context>> {
                         if args.len() > 0 {
                             let editor = PTYListEditor::new(
                                 ctx,
-                                args[0].clone(),
+                                (args[0].clone().0)[0].clone(),
                                 Some(','),
                                 depth + 1
                             );
@@ -125,7 +125,7 @@ pub fn init_editor_ctx(parent: Arc<RwLock<Context>>) -> Arc<RwLock<Context>> {
                     TypeTerm::Type {
                         id: ctx.read().unwrap().get_typeid("List").unwrap(),
                         args: vec![
-                            TypeTerm::new(ctx.read().unwrap().get_typeid("Char").unwrap())
+                            TypeTerm::new(ctx.read().unwrap().get_typeid("Char").unwrap()).into()
                         ]
                     },
                     depth+1
@@ -173,7 +173,7 @@ pub fn init_editor_ctx(parent: Arc<RwLock<Context>>) -> Arc<RwLock<Context>> {
                     TypeTerm::Type {
                         id: ctx.read().unwrap().get_typeid("List").unwrap(),
                         args: vec![
-                            TypeTerm::new(ctx.read().unwrap().get_typeid("Char").unwrap())
+                            TypeTerm::new(ctx.read().unwrap().get_typeid("Char").unwrap()).into()
                         ]
                     },
                     depth+1
@@ -215,9 +215,9 @@ pub fn init_math_ctx(parent: Arc<RwLock<Context>>) -> Arc<RwLock<Context>> {
                         id: _, args
                     } => {
                         if args.len() > 0 {
-                            match args[0] {
+                            match (args[0].0)[0] {
                                 TypeTerm::Num(radix) => {
-                                    let node = DigitEditor::new(ctx.clone(), radix as u32).into_node(depth);                                    
+                                    let node = DigitEditor::new(ctx.clone(), radix as u32).into_node(depth);
                                     Some(
                                         node
                                     )
@@ -252,7 +252,7 @@ pub fn init_math_ctx(parent: Arc<RwLock<Context>>) -> Arc<RwLock<Context>> {
                         id: _, args
                     } => {
                         if args.len() > 0 {
-                            match args[0] {
+                            match (args[0].0)[0] {
                                 TypeTerm::Num(_radix) => {
                                     let pty_editor = PTYListEditor::from_editor(
                                         editor,
@@ -291,7 +291,7 @@ pub fn init_math_ctx(parent: Arc<RwLock<Context>>) -> Arc<RwLock<Context>> {
                         id: _, args
                     } => {
                         if args.len() > 0 {
-                            match args[0] {
+                            match (args[0].0)[0] {
                                 TypeTerm::Num(radix) => {
 
                                     let mut node = Context::make_node(
@@ -302,6 +302,7 @@ pub fn init_math_ctx(parent: Arc<RwLock<Context>>) -> Arc<RwLock<Context>> {
                                                 TypeTerm::new(ctx.read().unwrap().get_typeid("Digit").unwrap())
                                                     .num_arg(radix)
                                                     .clone()
+                                                    .into()
                                             ]
                                         },
                                         depth+1
diff --git a/nested/src/type_system/mod.rs b/nested/src/type_system/mod.rs
index a4c590a..4446a91 100644
--- a/nested/src/type_system/mod.rs
+++ b/nested/src/type_system/mod.rs
@@ -1,13 +1,17 @@
-
-pub mod type_term;
-pub mod repr_tree;
 pub mod context;
+
+pub mod dict;
+pub mod term;
+pub mod ladder;
+pub mod repr_tree;
 pub mod make_editor;
-//pub mod type_term_editor;
+//pub mod editor;
 
 pub use {
-    repr_tree::{ReprTree},
-    type_term::{TypeDict, TypeID, TypeTerm, TypeLadder},
+    dict::*,
+    ladder::*,
+    repr_tree::*,
+    term::*,
     context::{Context, MorphismMode, MorphismType, MorphismTypePattern},
 //    type_term_editor::TypeTermEditor,
     make_editor::*
diff --git a/nested/src/type_system/type_term.rs b/nested/src/type_system/term.rs
similarity index 50%
rename from nested/src/type_system/type_term.rs
rename to nested/src/type_system/term.rs
index bae86b6..056b0be 100644
--- a/nested/src/type_system/type_term.rs
+++ b/nested/src/type_system/term.rs
@@ -1,66 +1,36 @@
-use {crate::utils::Bimap, std::collections::HashMap};
-
-//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
-
-pub type TypeID = u64;
-
-#[derive(Clone)]
-pub struct TypeLadder(pub Vec<TypeTerm>);
-
-impl From<Vec<TypeTerm>> for TypeLadder {
-    fn from(l: Vec<TypeTerm>) -> Self {
-        TypeLadder(l)
-    }
-}
-
-impl TypeLadder {
-    /// if compatible, returns the number of descents neccesary
-    pub fn is_compatible_with(&self, other: &TypeLadder) -> Option<usize> {
-        if let Some(other_top_type) = other.0.first() {
-            for (i, t) in self.0.iter().enumerate() {
-                if t == other_top_type {
-                    return Some(i);
-                }
-            }
-
-            None
-        } else {
-            None
-        }
-    }
-
-    pub fn is_matching_repr(&self, other: &TypeLadder) -> Result<usize, Option<(usize, usize)>> {
-        if let Some(start) = self.is_compatible_with(other) {
-            for (i, (t1, t2)) in self.0.iter().skip(start).zip(other.0.iter()).enumerate() {
-                if t1 != t2 {
-                    return Err(Some((start, i)));
-                }
-            }
-
-            Ok(start)
-        } else {
-            Err(None)
-        }
-    }
-}
+use {
+    crate::{
+        type_system::{TypeLadder, TypeID}
+    },
+    std::collections::HashMap
+};
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
 
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
 pub enum TypeTerm {
-    Type { id: TypeID, args: Vec<TypeTerm> },
+    Type {
+        id: u64,
+        args: Vec< TypeLadder >
+    },
+    Var(u64),
     Num(i64),
-//    Var(u64),
+    Char(char)
 }
 
+//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
+
 impl TypeTerm {
     pub fn new(id: TypeID) -> Self {
-        TypeTerm::Type { id, args: vec![] }
+        match id {
+            TypeID::Fun(id) => TypeTerm::Type { id, args: vec![] },
+            TypeID::Var(_) => {unreachable!();}
+        }
     }
 
-    pub fn arg(&mut self, t: TypeTerm) -> &mut Self {
+    pub fn arg(&mut self, t: impl Into<TypeLadder>) -> &mut Self {
         if let TypeTerm::Type { id: _, args } = self {
-            args.push(t);
+            args.push(t.into());
         }
 
         self
@@ -69,8 +39,12 @@ impl TypeTerm {
     pub fn num_arg(&mut self, v: i64) -> &mut Self {
         self.arg(TypeTerm::Num(v))
     }
- 
-    pub fn from_str(s: &str, names: &HashMap<String, u64>) -> Option<Self> {
+
+    pub fn char_arg(&mut self, c: char) -> &mut Self {
+        self.arg(TypeTerm::Char(c))
+    }
+
+    pub fn from_str(s: &str, names: &HashMap<String, TypeID>) -> Option<Self> {
         let mut term_stack = Vec::<Option<TypeTerm>>::new();
 
         for token in s.split_whitespace() {
@@ -100,13 +74,13 @@ impl TypeTerm {
                                 f.num_arg(i64::from_str_radix(atom, 10).unwrap());
                             } else {
                                 f.arg(TypeTerm::new(
-                                    *names.get(atom).expect(&format!("invalid atom {}", atom)),
+                                    names.get(atom).expect(&format!("invalid atom {}", atom)).clone(),
                                 ));
                             }
                         }
                         None => {
                             *f = Some(TypeTerm::new(
-                                *names.get(atom).expect(&format!("invalid atom {}", atom)),
+                                names.get(atom).expect(&format!("invalid atom {}", atom)).clone(),
                             ));
                         }
                     }
@@ -118,36 +92,38 @@ impl TypeTerm {
     }
 
     // only adds parenthesis where args.len > 0
-    pub fn to_str1(&self, names: &HashMap<u64, String>) -> String {
+    pub fn to_str1(&self, names: &HashMap<TypeID, String>) -> String {
         match self {
             TypeTerm::Type { id, args } => {
                 if args.len() > 0 {
                     format!(
-                        "( {} {})",
-                        names[id],
+                        "({}{})",
+                        names[&TypeID::Fun(*id)],
                         if args.len() > 0 {
                             args.iter().fold(String::new(), |str, term| {
-                                format!("{}{} ", str, term.to_str1(names))
+                                format!(" {}{}", str, term.to_str1(names))
                             })
                         } else {
                             String::new()
                         }
                     )
                 } else {
-                    names[id].clone()
+                    names[&TypeID::Fun(*id)].clone()
                 }
             }
 
             TypeTerm::Num(n) => format!("{}", n),
+            TypeTerm::Char(c) => format!("'{}'", c),
+            TypeTerm::Var(varid) => format!("T"),
         }
     }
 
     // always adds an enclosing pair of parenthesis
-    pub fn to_str(&self, names: &HashMap<u64, String>) -> String {
+    pub fn to_str(&self, names: &HashMap<TypeID, String>) -> String {
         match self {
             TypeTerm::Type { id, args } => format!(
                 "( {} {})",
-                names[id],
+                names[&TypeID::Fun(*id)],
                 if args.len() > 0 {
                     args.iter().fold(String::new(), |str, term| {
                         format!("{}{} ", str, term.to_str1(names))
@@ -158,47 +134,8 @@ impl TypeTerm {
             ),
 
             TypeTerm::Num(n) => format!("{}", n),
+            TypeTerm::Char(c) => format!("'{}'", c),
+            TypeTerm::Var(varid) => format!("T"),
         }
     }
 }
-
-//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>
-
-pub struct TypeDict {
-    typenames: Bimap<String, u64>,
-    type_id_counter: TypeID,
-}
-
-impl TypeDict {
-    pub fn new() -> Self {
-        TypeDict {
-            typenames: Bimap::new(),
-            type_id_counter: 0,
-        }
-    }
-
-    pub fn add_typename(&mut self, tn: String) -> TypeID {
-        let tyid = self.type_id_counter;
-        self.type_id_counter += 1;
-        self.typenames.insert(tn, tyid);
-        tyid
-    }
-
-    pub fn get_typename(&self, tid: &u64) -> Option<String> {
-        self.typenames.my.get(tid).cloned()
-    }
-
-    pub fn get_typeid(&self, tn: &String) -> Option<TypeID> {
-        self.typenames.mλ.get(tn).cloned()
-    }
-
-    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)
-    }
-}
-
-//<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>