diff --git a/src/custom_errors.rs b/src/custom_errors.rs
index d0002a9..c709be6 100644
--- a/src/custom_errors.rs
+++ b/src/custom_errors.rs
@@ -11,3 +11,18 @@ pub enum DFAError {
     #[error("Invalid symbol: {0}")]
     InvalidSymbol(&'static str),
 }
+
+#[derive(Debug, Error)]
+pub enum NFAError {
+    #[error("Already Existing Transition {0}")]
+    ExistingTransition(&'static str),
+}
+
+#[derive(Debug, Error)]
+pub enum AutomatonError {
+    #[error("DFA Error {0}")]
+    DFAError(DFAError),
+
+    #[error("NFA Error {0}")]
+    NFAError(NFAError),
+}
diff --git a/src/d_transition_function.rs b/src/d_transition_function.rs
index 7dc1e7a..a2c2007 100644
--- a/src/d_transition_function.rs
+++ b/src/d_transition_function.rs
@@ -3,7 +3,9 @@
 use std::collections::HashMap;
 
 use crate::{
-    custom_errors::DFAError, globals::State, symbol_table::Symbol,
+    custom_errors::{AutomatonError, DFAError},
+    globals::State,
+    symbol_table::Symbol,
     transition_function::BasicFunctionsForTransitions,
 };
 
@@ -22,19 +24,19 @@ impl BasicFunctionsForTransitions for DTransitionFunction {
         state: &State,
         symbol: &Symbol,
         next_state: &State,
-    ) -> Result<(), crate::custom_errors::DFAError> {
+    ) -> Result<(), AutomatonError> {
         if *symbol == Symbol::Epsilon {
-            return Err(DFAError::InvalidTransition(
+            return Err(AutomatonError::DFAError(DFAError::InvalidTransition(
                 "Epsilon should not be present in DFA Transitions",
-            ));
+            )));
         }
 
         let entry = self.f.entry(*state).or_insert(HashMap::new());
 
         if entry.contains_key(symbol) {
-            return Err(DFAError::InvalidTransition(
+            return Err(AutomatonError::DFAError(DFAError::InvalidTransition(
                 "Adding more than one state for the same transition for DFA",
-            ));
+            )));
         }
 
         entry.insert(*symbol, *next_state);
@@ -49,16 +51,17 @@ impl BasicFunctionsForTransitions for DTransitionFunction {
         on_states.reverse();
 
         for &curr_state in on_states.iter() {
-            let mut new_transitions: HashMap<Symbol, State> = HashMap::new();
+            if let Some((state, symbol_state_map)) = self.f.remove_entry(&curr_state) {
+                let mut new_transitions: HashMap<Symbol, State> = HashMap::new();
 
-            // (curr_state, symbol) -> next_state
-            for (symbol, next_state) in self.f[&curr_state].iter() {
-                new_transitions.insert(*symbol, *next_state + increment);
-            }
+                // (state, symbol) -> next_state
+                for (symbol, next_state) in symbol_state_map.iter() {
+                    new_transitions.insert(*symbol, *next_state + increment);
+                }
 
-            // update the transitions
-            self.f.insert(curr_state + increment, new_transitions);
-            self.f.remove_entry(&curr_state);
+                // update the transitions
+                self.f.insert(state + increment, new_transitions);
+            }
         }
     }
 }
diff --git a/src/n_transition_function.rs b/src/n_transition_function.rs
index 99aeb0e..92b7efb 100644
--- a/src/n_transition_function.rs
+++ b/src/n_transition_function.rs
@@ -1,9 +1,10 @@
 #![allow(dead_code)]
 
 use crate::{
-    custom_errors::DFAError,
+    custom_errors::{AutomatonError, NFAError},
     globals::State,
-    symbol_table::{Symbol, SymbolTable},
+    symbol_table::Symbol,
+    transition_function::BasicFunctionsForTransitions,
 };
 use std::collections::{HashMap, HashSet};
 
@@ -12,7 +13,98 @@ pub struct NTransitionFunction {
     f: HashMap<State, HashMap<Symbol, HashSet<State>>>,
 }
 
+impl BasicFunctionsForTransitions for NTransitionFunction {
+    fn new() -> Self {
+        NTransitionFunction { f: HashMap::new() }
+    }
+
+    fn extend(&mut self, increment: usize) {
+        //
+        let mut on_states: Vec<State> = self.f.keys().map(|&val| val).collect();
+        on_states.sort();
+        // going through keys in decreasing order, in order to avoid overlapping issue
+        on_states.reverse();
+
+        for &curr_state in on_states.iter() {
+            if let Some((state, symbol_to_next_state_set_map)) = self.f.remove_entry(&curr_state) {
+                let mut new_transitions: HashMap<Symbol, HashSet<State>> = HashMap::new();
+
+                // (curr_state, symbol) -> next_state_set
+                for (symbol, next_state_set) in symbol_to_next_state_set_map.iter() {
+                    // new_transitions.insert(*symbol, *next_state + increment);
+                    let mut new_next_state_set = HashSet::new();
+
+                    for &next_state in next_state_set.iter() {
+                        new_next_state_set.insert(next_state + increment);
+                    }
+
+                    new_transitions.insert(*symbol, new_next_state_set);
+                }
+
+                // update the transitions
+                self.f.insert(state + increment, new_transitions);
+            }
+        }
+    }
+
+    fn add_transition(
+        &mut self,
+        state: &State,
+        symbol: &Symbol,
+        next_state: &State,
+    ) -> Result<(), AutomatonError> {
+        let state_transitions = self.f.entry(*state).or_insert(HashMap::new());
+        let state_symbol_transitions = state_transitions.entry(*symbol).or_insert(HashSet::new());
+
+        if state_symbol_transitions.contains(next_state) {
+            return Err(AutomatonError::NFAError(NFAError::ExistingTransition("")));
+        }
+
+        state_symbol_transitions.insert(*next_state);
+        Ok(())
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
+
+    #[test]
+    fn check_normal_and_multiple_transitions() {
+        let mut nt = NTransitionFunction::new();
+        let _ = nt
+            .add_transition(&0, &Symbol::Character('a'), &1)
+            .unwrap_or_else(|err| panic!("Error in adding transition : {}", err.to_string()));
+        let _ = nt
+            .add_transition(&0, &Symbol::Character('a'), &2)
+            .unwrap_or_else(|err| panic!("Error in adding transition : {}", err.to_string()));
+
+        assert!(nt.f.contains_key(&0));
+        assert!(nt.f[&0].contains_key(&Symbol::Character('a')));
+        assert!(nt.f[&0][&Symbol::Character('a')].contains(&1));
+        assert!(nt.f[&0][&Symbol::Character('a')].contains(&2));
+    }
+
+    #[test]
+    fn check_adding_epsilon_transition() {
+        let mut nt = NTransitionFunction::new();
+
+        let _ = nt
+            .add_transition(&0, &Symbol::Epsilon, &2)
+            .unwrap_or_else(|err| panic!("Error in adding transition : {}", err.to_string()));
+        assert!(nt.f.contains_key(&0));
+        assert!(nt.f[&0].contains_key(&Symbol::Epsilon));
+        assert!(nt.f[&0][&Symbol::Epsilon].contains(&2));
+    }
+
+    #[test]
+    fn check_adding_same_transition() {
+        let mut nt = NTransitionFunction::new();
+        let _ = nt
+            .add_transition(&0, &Symbol::Character('a'), &1)
+            .unwrap_or_else(|err| panic!("Error in adding transition : {}", err.to_string()));
+        let result = nt.add_transition(&0, &Symbol::Character('a'), &1);
+
+        assert!(result.is_err_and(|err| err.to_string().contains("Existing Transition")));
+    }
 }
diff --git a/src/transition_function.rs b/src/transition_function.rs
index 29a068f..71d52dc 100644
--- a/src/transition_function.rs
+++ b/src/transition_function.rs
@@ -3,7 +3,7 @@
 use std::collections::HashSet;
 use std::ops::Index;
 
-use crate::custom_errors::DFAError;
+use crate::custom_errors::AutomatonError;
 use crate::d_transition_function;
 use crate::globals::State;
 use crate::n_transition_function;
@@ -26,7 +26,7 @@ pub trait BasicFunctionsForTransitions {
         state: &State,
         symbol: &Symbol,
         next_state: &State,
-    ) -> Result<(), DFAError>;
+    ) -> Result<(), AutomatonError>;
 
     fn extend(&mut self, increment: usize);
 }