diff --git a/schala-lang/src/typechecking.rs b/schala-lang/src/typechecking.rs
index dac6ca4..f8d99b4 100644
--- a/schala-lang/src/typechecking.rs
+++ b/schala-lang/src/typechecking.rs
@@ -1,4 +1,5 @@
 use std::rc::Rc;
+use std::collections::HashMap;
 /*
 use std::collections::{HashSet, HashMap};
 use std::collections::hash_set::Union;
@@ -29,6 +30,18 @@ enum TConst {
   Custom(String)
 }
 
+#[derive(Debug, PartialEq, Clone)]
+struct Scheme {
+  names: Vec<TypeName>,
+  ty: Type,
+}
+
+#[derive(Debug, PartialEq, Clone)]
+struct Substitution(HashMap<TypeName, Type>);
+
+#[derive(Debug, PartialEq, Clone)]
+struct TypeEnv(HashMap<TypeName, Scheme>);
+
 pub struct TypeContext<'a> {
   values: StateStack<'a, TypeName, Type>
 }