diff --git a/src/steiner_tree.rs b/src/steiner_tree.rs
index c8984dd..6e2443d 100644
--- a/src/steiner_tree.rs
+++ b/src/steiner_tree.rs
@@ -17,7 +17,7 @@ use {
 pub struct SteinerTree {
     weight: u64,
     goals: Vec< TypeTerm >,
-    edges: Vec< MorphismType >,
+    pub edges: Vec< MorphismType >,
 }
 
 impl SteinerTree {
diff --git a/src/test/curry.rs b/src/test/curry.rs
index c728a37..a814ab2 100644
--- a/src/test/curry.rs
+++ b/src/test/curry.rs
@@ -1,12 +1,12 @@
 use {
-    crate::{dict::*}
+    crate::{dict::*, parser::*}
 };
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>\\
 
 #[test]
 fn test_curry() {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
 
     assert_eq!(
         dict.parse("<A B C>").unwrap().curry(),
@@ -33,7 +33,7 @@ fn test_curry() {
 
 #[test]
 fn test_decurry() {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
 
     assert_eq!(
         dict.parse("<<A B> C>").unwrap().decurry(),
@@ -47,7 +47,7 @@ fn test_decurry() {
         dict.parse("<<<<<<<<<<A B> C> D> E> F> G> H> I> J> K>").unwrap().decurry(),
         dict.parse("<A B C D E F G H I J K>").unwrap()
     );
-    
+
     assert_eq!(
         dict.parse("<<A~X B> C>").unwrap().decurry(),
         dict.parse("<A~X B C>").unwrap()
diff --git a/src/test/lnf.rs b/src/test/lnf.rs
index 1c81a55..4b2a7c2 100644
--- a/src/test/lnf.rs
+++ b/src/test/lnf.rs
@@ -1,8 +1,8 @@
-use crate::dict::TypeDict;
+use crate::{dict::{BimapTypeDict}, parser::*};
 
 #[test]
 fn test_flat() {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
 
     assert!( dict.parse("A").expect("parse error").is_flat() );
     assert!( dict.parse("10").expect("parse error").is_flat() );
@@ -17,7 +17,7 @@ fn test_flat() {
 
 #[test]
 fn test_normalize() {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
 
     assert_eq!(
         dict.parse("A~B~C").expect("parse error").normalize(),
@@ -54,4 +54,3 @@ fn test_normalize() {
     );
 
 }
-
diff --git a/src/test/morphism.rs b/src/test/morphism.rs
index b908101..309d881 100644
--- a/src/test/morphism.rs
+++ b/src/test/morphism.rs
@@ -1,5 +1,5 @@
 use {
-    crate::{dict::*, morphism::*, steiner_tree::*, TypeTerm}
+    crate::{dict::*, parser::*, unparser::*, morphism::*, steiner_tree::*, TypeTerm}
 };
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>\\
@@ -27,8 +27,8 @@ impl Morphism for DummyMorphism {
     }
 }
 
-fn morphism_test_setup() -> ( TypeDict, MorphismBase<DummyMorphism> ) {
-    let mut dict = TypeDict::new();
+fn morphism_test_setup() -> ( BimapTypeDict, MorphismBase<DummyMorphism> ) {
+    let mut dict = BimapTypeDict::new();
     let mut base = MorphismBase::<DummyMorphism>::new( dict.add_typename("Seq".into()) );
 
     dict.add_varname("Radix".into());
@@ -118,7 +118,7 @@ fn test_morphism_path() {
         Some((
                 DummyMorphism(MorphismType{
                     src_type: dict.parse("<Seq <Digit Radix> ~ Char>").unwrap(),
-                    dst_type: dict.parse("<Seq <Digit Radix> ~ ℤ_2^64 ~ machine.UInt64>").unwrap()                
+                    dst_type: dict.parse("<Seq <Digit Radix> ~ ℤ_2^64 ~ machine.UInt64>").unwrap()
                 }),
 
                 dict.parse("Symbol ~ ℕ ~ <PosInt 10 BigEndian> ~ <Seq <Digit 10>>").unwrap(),
@@ -145,12 +145,12 @@ fn test_steiner_tree() {
         // destination reprs
         vec![
             dict.parse("ℕ ~ <PosInt 2 BigEndian> ~ <Seq <Digit 2> ~ Char>").unwrap(),
-            dict.parse("ℕ ~ <PosInt 10 LittleEndian> ~ <Seq <Digit 10> ~ Char>").unwrap(),            
+            dict.parse("ℕ ~ <PosInt 10 LittleEndian> ~ <Seq <Digit 10> ~ Char>").unwrap(),
             dict.parse("ℕ ~ <PosInt 16 LittleEndian> ~ <Seq <Digit 16> ~ Char>").unwrap()
         ]
     );
 
-    if let Some(solution) = steiner_tree_problem.solve_bfs( &dict, &base ) {
+    if let Some(solution) = steiner_tree_problem.solve_bfs( &base ) {
         for e in solution.edges.iter() {
             eprintln!(" :: {}\n--> {}", dict.unparse(&e.src_type), dict.unparse(&e.dst_type));
         }
@@ -158,4 +158,3 @@ fn test_steiner_tree() {
         eprintln!("no solution");
     }
 }
-
diff --git a/src/test/parser.rs b/src/test/parser.rs
index 1166229..f650ae3 100644
--- a/src/test/parser.rs
+++ b/src/test/parser.rs
@@ -7,7 +7,7 @@ use {
 
 #[test]
 fn test_parser_id() {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
 
     dict.add_varname("T".into());
 
@@ -26,7 +26,7 @@ fn test_parser_id() {
 fn test_parser_num() {
     assert_eq!(
         Ok(TypeTerm::Num(1234)),
-        TypeDict::new().parse("1234")
+        BimapTypeDict::new().parse("1234")
     );
 }
 
@@ -34,21 +34,21 @@ fn test_parser_num() {
 fn test_parser_char() {
     assert_eq!(
         Ok(TypeTerm::Char('x')),
-        TypeDict::new().parse("'x'")
+        BimapTypeDict::new().parse("'x'")
     );
 }
 
 #[test]
 fn test_parser_app() {
     assert_eq!(
-        TypeDict::new().parse("<A B>"),
+        BimapTypeDict::new().parse("<A B>"),
         Ok(TypeTerm::App(vec![
             TypeTerm::TypeID(TypeID::Fun(0)),
             TypeTerm::TypeID(TypeID::Fun(1)),
         ]))
     );
     assert_eq!(
-        TypeDict::new().parse("<A B C>"),
+        BimapTypeDict::new().parse("<A B C>"),
         Ok(TypeTerm::App(vec![
             TypeTerm::TypeID(TypeID::Fun(0)),
             TypeTerm::TypeID(TypeID::Fun(1)),
@@ -60,7 +60,7 @@ fn test_parser_app() {
 #[test]
 fn test_parser_unexpected_close() {
     assert_eq!(
-        TypeDict::new().parse(">"),
+        BimapTypeDict::new().parse(">"),
         Err(ParseError::UnexpectedClose)
     );
 }
@@ -68,7 +68,7 @@ fn test_parser_unexpected_close() {
 #[test]
 fn test_parser_unexpected_token() {
     assert_eq!(
-        TypeDict::new().parse("A B"),
+        BimapTypeDict::new().parse("A B"),
         Err(ParseError::UnexpectedToken)
     );
 }
@@ -76,14 +76,14 @@ fn test_parser_unexpected_token() {
 #[test]
 fn test_parser_ladder() {
     assert_eq!(
-        TypeDict::new().parse("A~B"),
+        BimapTypeDict::new().parse("A~B"),
         Ok(TypeTerm::Ladder(vec![
             TypeTerm::TypeID(TypeID::Fun(0)),
             TypeTerm::TypeID(TypeID::Fun(1)),
         ]))
     );
     assert_eq!(
-        TypeDict::new().parse("A~B~C"),
+        BimapTypeDict::new().parse("A~B~C"),
         Ok(TypeTerm::Ladder(vec![
             TypeTerm::TypeID(TypeID::Fun(0)),
             TypeTerm::TypeID(TypeID::Fun(1)),
@@ -95,7 +95,7 @@ fn test_parser_ladder() {
 #[test]
 fn test_parser_ladder_outside() {
     assert_eq!(
-        TypeDict::new().parse("<A B>~C"),
+        BimapTypeDict::new().parse("<A B>~C"),
         Ok(TypeTerm::Ladder(vec![
             TypeTerm::App(vec![
                 TypeTerm::TypeID(TypeID::Fun(0)),
@@ -103,13 +103,13 @@ fn test_parser_ladder_outside() {
             ]),
             TypeTerm::TypeID(TypeID::Fun(2)),
         ]))
-    );    
+    );
 }
 
 #[test]
 fn test_parser_ladder_inside() {
     assert_eq!(
-        TypeDict::new().parse("<A B~C>"),
+        BimapTypeDict::new().parse("<A B~C>"),
         Ok(TypeTerm::App(vec![
             TypeTerm::TypeID(TypeID::Fun(0)),
             TypeTerm::Ladder(vec![
@@ -117,13 +117,13 @@ fn test_parser_ladder_inside() {
                 TypeTerm::TypeID(TypeID::Fun(2)),
             ])
         ]))
-    );    
+    );
 }
 
 #[test]
 fn test_parser_ladder_between() {
     assert_eq!(
-        TypeDict::new().parse("<A B~<C D>>"),
+        BimapTypeDict::new().parse("<A B~<C D>>"),
         Ok(TypeTerm::App(vec![
             TypeTerm::TypeID(TypeID::Fun(0)),
             TypeTerm::Ladder(vec![
@@ -134,14 +134,14 @@ fn test_parser_ladder_between() {
                 ])
             ])
         ]))
-    );    
+    );
 }
 
 
 #[test]
 fn test_parser_ladder_large() {
     assert_eq!(
-        TypeDict::new().parse(
+        BimapTypeDict::new().parse(
             "<Seq Date
                   ~<TimeSince UnixEpoch>
                   ~<Duration Seconds>
@@ -203,4 +203,3 @@ fn test_parser_ladder_large() {
         )
     );
 }
-
diff --git a/src/test/pnf.rs b/src/test/pnf.rs
index e668849..a1d5a33 100644
--- a/src/test/pnf.rs
+++ b/src/test/pnf.rs
@@ -1,8 +1,8 @@
-use crate::dict::TypeDict;
+use crate::{dict::BimapTypeDict, parser::*};
 
 #[test]
 fn test_param_normalize() {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
 
     assert_eq!(
         dict.parse("A~B~C").expect("parse error"),
@@ -56,4 +56,3 @@ fn test_param_normalize() {
                .param_normalize(),
     );
 }
-
diff --git a/src/test/substitution.rs b/src/test/substitution.rs
index 7959b08..e8906b9 100644
--- a/src/test/substitution.rs
+++ b/src/test/substitution.rs
@@ -1,6 +1,6 @@
 
 use {
-    crate::{dict::*, term::*},
+    crate::{dict::*, term::*, parser::*, unparser::*},
     std::iter::FromIterator
 };
 
@@ -8,7 +8,7 @@ use {
 
 #[test]
 fn test_subst() {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
 
     let mut σ = std::collections::HashMap::new();
 
@@ -29,4 +29,3 @@ fn test_subst() {
         dict.parse("<Seq ℕ~<Seq Char>>").unwrap()
     );
 }
-
diff --git a/src/test/subtype.rs b/src/test/subtype.rs
index 08cc5c7..c993063 100644
--- a/src/test/subtype.rs
+++ b/src/test/subtype.rs
@@ -1,8 +1,8 @@
-use crate::dict::TypeDict;
+use crate::{dict::BimapTypeDict, parser::*, unparser::*};
 
 #[test]
 fn test_semantic_subtype() {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
 
     assert_eq!(
         dict.parse("A~B~C").expect("parse error")
@@ -19,11 +19,11 @@ fn test_semantic_subtype() {
             ),
         Some((0, dict.parse("A~B1~C1").expect("parse errror")))
     );
-    
+
     assert_eq!(
         dict.parse("A~B~C1").expect("parse error")
             .is_semantic_subtype_of(
-                &dict.parse("B~C2").expect("parse errror")  
+                &dict.parse("B~C2").expect("parse errror")
             ),
         Some((1, dict.parse("B~C1").expect("parse errror")))
     );
@@ -31,12 +31,12 @@ fn test_semantic_subtype() {
 
 #[test]
 fn test_syntactic_subtype() {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
 
     assert_eq!(
         dict.parse("A~B~C").expect("parse error")
             .is_syntactic_subtype_of(
-                &dict.parse("A~B~C").expect("parse errror")  
+                &dict.parse("A~B~C").expect("parse errror")
             ),
         Ok(0)
     );
@@ -44,7 +44,7 @@ fn test_syntactic_subtype() {
     assert_eq!(
         dict.parse("A~B~C").expect("parse error")
             .is_syntactic_subtype_of(
-                &dict.parse("B~C").expect("parse errror")  
+                &dict.parse("B~C").expect("parse errror")
             ),
         Ok(1)
     );
@@ -52,7 +52,7 @@ fn test_syntactic_subtype() {
     assert_eq!(
         dict.parse("A~B~C~D~E").expect("parse error")
             .is_syntactic_subtype_of(
-                &dict.parse("C~D").expect("parse errror")  
+                &dict.parse("C~D").expect("parse errror")
             ),
         Ok(2)
     );
@@ -60,7 +60,7 @@ fn test_syntactic_subtype() {
     assert_eq!(
         dict.parse("A~B~C~D~E").expect("parse error")
             .is_syntactic_subtype_of(
-                &dict.parse("C~G").expect("parse errror")  
+                &dict.parse("C~G").expect("parse errror")
             ),
         Err((2,3))
     );
@@ -68,7 +68,7 @@ fn test_syntactic_subtype() {
     assert_eq!(
         dict.parse("A~B~C~D~E").expect("parse error")
             .is_syntactic_subtype_of(
-                &dict.parse("G~F~K").expect("parse errror")  
+                &dict.parse("G~F~K").expect("parse errror")
             ),
         Err((0,0))
     );
@@ -94,4 +94,3 @@ fn test_syntactic_subtype() {
         Ok(4)
     );
 }
-
diff --git a/src/test/unification.rs b/src/test/unification.rs
index 6c55a80..56e88e2 100644
--- a/src/test/unification.rs
+++ b/src/test/unification.rs
@@ -1,13 +1,13 @@
 
 use {
-    crate::{dict::*, term::*, unification::*},
+    crate::{dict::*, parser::*, unparser::*, term::*, unification::*},
     std::iter::FromIterator
 };
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>\\
 
 fn test_unify(ts1: &str, ts2: &str, expect_unificator: bool) {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
     dict.add_varname(String::from("T"));
     dict.add_varname(String::from("U"));
     dict.add_varname(String::from("V"));
@@ -33,7 +33,7 @@ fn test_unify(ts1: &str, ts2: &str, expect_unificator: bool) {
 
 #[test]
 fn test_unification_error() {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
     dict.add_varname(String::from("T"));
 
     assert_eq!(
@@ -89,7 +89,7 @@ fn test_unification() {
         true
     );
 
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
 
     dict.add_varname(String::from("T"));
     dict.add_varname(String::from("U"));
@@ -129,10 +129,9 @@ fn test_unification() {
     );
 }
 
-
 #[test]
 fn test_subtype_unification() {
-    let mut dict = TypeDict::new();
+    let mut dict = BimapTypeDict::new();
 
     dict.add_varname(String::from("T"));
     dict.add_varname(String::from("U"));