diff --git a/src/main.rs b/src/main.rs
index 425d79e..535e5ca 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -8,55 +8,6 @@ enum RegExp {
     Kleene(Box<RegExp>),
 }
 
-
-// Derivatives
-
-fn is_nullable (r : &RegExp) -> bool {
-    match r {
-        RegExp::Epsilon => true,
-        RegExp::Kleene(_) => true,
-        RegExp::Union(r1, r2) => is_nullable(&*r1) | is_nullable(&*r2),
-        RegExp::Concat(r1, r2) => is_nullable(&*r1) & is_nullable(&*r2),
-        _ => false,
-    }
-}
-
-fn derivative(r : &RegExp, a : char) -> RegExp {
-    match r {
-        RegExp::Empt => RegExp::Empt,
-        RegExp::Epsilon => RegExp::Empt,
-        RegExp::Char(c) => if *c == a {
-            RegExp::Epsilon
-        } else { RegExp::Empt },
-        RegExp::Union(r1, r2) =>
-            RegExp::Union(Box::new(derivative(&*r1, a)), Box::new(derivative(&*r2, a))),
-        RegExp::Kleene(r) =>
-            RegExp::Concat(Box::new(derivative(&*r, a)),
-                           Box::new(RegExp::Kleene(Box::new(*r.clone())))),
-        RegExp::Concat(r1, r2) => {
-            let r : RegExp = RegExp::Concat(Box::new(derivative(&*r1, a)),
-                                            Box::new(*r2.clone()));
-            if is_nullable(&*r1) {
-                RegExp::Union(Box::new(derivative(&*r2, a)), Box::new(r))
-            } else {
-                r
-            }
-        }
-        _ => RegExp::Empt,
-    }
-}
-
-impl RegExp {
-    fn match_string(self : RegExp, s : &String) -> bool {
-        let chrs = s.chars();
-        let mut rs : RegExp = self;
-        for c in chrs {
-            rs = derivative(&rs, c); 
-        }
-        is_nullable(&rs)
-    }
-}
-
 use std::iter::Peekable;
 use std::str::Chars;
 
@@ -138,6 +89,55 @@ impl RegExp {
         }
     }
 }
+
+// Derivatives
+
+fn is_nullable (r : &RegExp) -> bool {
+    match r {
+        RegExp::Epsilon => true,
+        RegExp::Kleene(_) => true,
+        RegExp::Union(r1, r2) => is_nullable(&*r1) | is_nullable(&*r2),
+        RegExp::Concat(r1, r2) => is_nullable(&*r1) & is_nullable(&*r2),
+        _ => false,
+    }
+}
+
+fn derivative(r : &RegExp, a : char) -> RegExp {
+    match r {
+        RegExp::Empt => RegExp::Empt,
+        RegExp::Epsilon => RegExp::Empt,
+        RegExp::Char(c) => if *c == a {
+            RegExp::Epsilon
+        } else { RegExp::Empt },
+        RegExp::Union(r1, r2) =>
+            RegExp::Union(Box::new(derivative(&*r1, a)), Box::new(derivative(&*r2, a))),
+        RegExp::Kleene(r) =>
+            RegExp::Concat(Box::new(derivative(&*r, a)),
+                           Box::new(RegExp::Kleene(Box::new(*r.clone())))),
+        RegExp::Concat(r1, r2) => {
+            let r : RegExp = RegExp::Concat(Box::new(derivative(&*r1, a)),
+                                            Box::new(*r2.clone()));
+            if is_nullable(&*r1) {
+                RegExp::Union(Box::new(derivative(&*r2, a)), Box::new(r))
+            } else {
+                r
+            }
+        }
+        _ => RegExp::Empt,
+    }
+}
+
+impl RegExp {
+    fn match_string(self : RegExp, s : &String) -> bool {
+        let chrs = s.chars();
+        let mut rs : RegExp = self;
+        for c in chrs {
+            rs = derivative(&rs, c); 
+        }
+        is_nullable(&rs)
+    }
+}
+
 fn main() {
     let s1 = RegExp::from(String::from("(ab|c)(ab)*"));
     let inp = String::from("abab");