diff --git a/lib/imbecile.rb b/lib/imbecile.rb
index 9524a48..2099602 100644
--- a/lib/imbecile.rb
+++ b/lib/imbecile.rb
@@ -4,6 +4,9 @@ require_relative "imbecile/cli"
 require_relative "imbecile/code_point_range"
 require_relative "imbecile/grammar"
 require_relative "imbecile/regex"
+require_relative "imbecile/regex/fa"
+require_relative "imbecile/regex/fa/state"
+require_relative "imbecile/regex/fa/state/transition"
 require_relative "imbecile/regex/dfa"
 require_relative "imbecile/regex/nfa"
 require_relative "imbecile/regex/unit"
diff --git a/lib/imbecile/regex/dfa.rb b/lib/imbecile/regex/dfa.rb
index 65a93cf..00db7f7 100644
--- a/lib/imbecile/regex/dfa.rb
+++ b/lib/imbecile/regex/dfa.rb
@@ -1,39 +1,10 @@
 module Imbecile
   class Regex
 
-    class DFA
-
-      class State
-
-        attr_reader :id
-
-        class Transition
-
-          attr_reader :code_point_range
-          attr_reader :destination
-
-          def initialize(code_point_range, destination)
-            @code_point_range = code_point_range
-            @destination = destination
-          end
-
-        end
-
-        attr_accessor :accepts
-        attr_reader :transitions
-
-        def initialize(id)
-          @id = id
-          @transitions = []
-        end
-
-        def add_transition(code_point_range, destination)
-          @transitions << Transition.new(code_point_range, destination)
-        end
-
-      end
+    class DFA < FA
 
       def initialize(nfas)
+        super()
         start_nfa = NFA.new
         nfas.each do |nfa|
           start_nfa.start_state.add_transition(nil, nfa.start_state)
@@ -48,30 +19,7 @@ module Imbecile
           @to_process.delete(state_set)
           process_nfa_state_set(state_set)
         end
-      end
-
-      def to_s
-        chr = lambda do |value|
-          if value < 32 || value > 127
-            "{#{value}}"
-          else
-            value.chr
-          end
-        end
-        rv = ""
-        @states.each_with_index do |state, state_id|
-          accepts_s = state.accepts ? " (#{state.accepts})" : ""
-          rv += "#{state_id}#{accepts_s}:\n"
-          state.transitions.each do |transition|
-            range_s = chr[transition.code_point_range.first]
-            if transition.code_point_range.size > 1
-              range_s += "-" + chr[transition.code_point_range.last]
-            end
-            accepts_s = transition.destination.accepts ? " (#{transition.destination.accepts})" : ""
-            rv += "  #{range_s} => #{transition.destination.id}#{accepts_s}\n"
-          end
-        end
-        rv
+        @start_state = @states[0]
       end
 
       private
@@ -80,7 +28,7 @@ module Imbecile
         unless @nfa_state_sets.include?(nfa_state_set)
           state_id = @states.size
           @nfa_state_sets[nfa_state_set] = state_id
-          @states << State.new(state_id)
+          @states << State.new
           @to_process << nfa_state_set
         end
       end
diff --git a/lib/imbecile/regex/fa.rb b/lib/imbecile/regex/fa.rb
new file mode 100644
index 0000000..d242bd5
--- /dev/null
+++ b/lib/imbecile/regex/fa.rb
@@ -0,0 +1,56 @@
+module Imbecile
+  class Regex
+
+    class FA
+
+      attr_reader :start_state
+
+      def initialize
+        @start_state = State.new
+      end
+
+      def to_s
+        chr = lambda do |value|
+          if value < 32 || value > 127
+            "{#{value}}"
+          else
+            value.chr
+          end
+        end
+        rv = ""
+        states = {start_state => 0}
+        to_visit = [start_state]
+        state_id = lambda do |state|
+          unless states.include?(state)
+            states[state] = states.values.max + 1
+            to_visit << state
+          end
+          states[state]
+        end
+        visit = lambda do |state|
+          accepts_s = state.accepts ? " *" : ""
+          rv += "#{state_id[state]}#{accepts_s}:\n"
+          state.transitions.each do |transition|
+            if transition.nil?
+              range_s = "nil"
+            else
+              range_s = chr[transition.code_point_range.first]
+              if transition.code_point_range.size > 1
+                range_s += "-" + chr[transition.code_point_range.last]
+              end
+            end
+            accepts_s = transition.destination.accepts ? " *" : ""
+            rv += "  #{range_s} => #{state_id[transition.destination]}#{accepts_s}\n"
+          end
+        end
+        while to_visit.size > 0
+          visit[to_visit[0]]
+          to_visit.slice!(0)
+        end
+        rv
+      end
+
+    end
+
+  end
+end
diff --git a/lib/imbecile/regex/fa/state.rb b/lib/imbecile/regex/fa/state.rb
new file mode 100644
index 0000000..ee4fab9
--- /dev/null
+++ b/lib/imbecile/regex/fa/state.rb
@@ -0,0 +1,53 @@
+module Imbecile
+  class Regex
+    class FA
+
+      class State
+
+        attr_accessor :accepts
+        attr_reader :transitions
+
+        def initialize
+          @transitions = []
+        end
+
+        def add_transition(code_point_range, destination)
+          @transitions << Transition.new(code_point_range, destination)
+        end
+
+        # Determine the set of states that can be reached by nil transitions.
+        # from this state.
+        #
+        # @return [Set<NFA::State>]
+        #   Set of states.
+        def nil_transition_states
+          states = Set[self]
+          analyze_state = lambda do |state|
+            state.nil_transitions.each do |transition|
+              unless states.include?(transition.destination)
+                states << transition.destination
+                analyze_state[transition.destination]
+              end
+            end
+          end
+          analyze_state[self]
+          states
+        end
+
+        def nil_transitions
+          @transitions.select do |transition|
+            transition.nil?
+          end
+        end
+
+        def cp_transitions
+          @transitions.reject do |transition|
+            transition.nil?
+          end
+        end
+
+      end
+
+    end
+  end
+end
diff --git a/lib/imbecile/regex/fa/state/transition.rb b/lib/imbecile/regex/fa/state/transition.rb
new file mode 100644
index 0000000..5bd0efb
--- /dev/null
+++ b/lib/imbecile/regex/fa/state/transition.rb
@@ -0,0 +1,25 @@
+module Imbecile
+  class Regex
+    class FA
+      class State
+
+        class Transition
+
+          attr_reader :code_point_range
+          attr_reader :destination
+
+          def initialize(code_point_range, destination)
+            @code_point_range = code_point_range
+            @destination = destination
+          end
+
+          def nil?
+            @code_point_range.nil?
+          end
+
+        end
+
+      end
+    end
+  end
+end
diff --git a/lib/imbecile/regex/nfa.rb b/lib/imbecile/regex/nfa.rb
index f5d97ae..824ed04 100644
--- a/lib/imbecile/regex/nfa.rb
+++ b/lib/imbecile/regex/nfa.rb
@@ -1,120 +1,15 @@
 module Imbecile
   class Regex
 
-    class NFA
+    class NFA < FA
 
-      class State
-
-        class Transition
-
-          attr_reader :code_point_range
-          attr_reader :destination
-
-          def initialize(code_point_range, destination)
-            @code_point_range = code_point_range
-            @destination = destination
-          end
-
-          def nil?
-            @code_point_range.nil?
-          end
-
-        end
-
-        attr_accessor :accepts
-        attr_reader :transitions
-
-        def initialize
-          @transitions = []
-        end
-
-        def add_transition(code_point_range, destination)
-          @transitions << Transition.new(code_point_range, destination)
-        end
-
-        # Determine the set of states that can be reached by nil transitions.
-        # from this state.
-        #
-        # @return [Set<NFA::State>]
-        #   Set of states.
-        def nil_transition_states
-          states = Set[self]
-          analyze_state = lambda do |state|
-            state.nil_transitions.each do |transition|
-              unless states.include?(transition.destination)
-                states << transition.destination
-                analyze_state[transition.destination]
-              end
-            end
-          end
-          analyze_state[self]
-          states
-        end
-
-        def nil_transitions
-          @transitions.select do |transition|
-            transition.nil?
-          end
-        end
-
-        def cp_transitions
-          @transitions.reject do |transition|
-            transition.nil?
-          end
-        end
-
-      end
-
-      attr_accessor :start_state
-
-      attr_accessor :end_state
+      attr_reader :end_state
 
       def initialize
-        @start_state = State.new
+        super()
         @end_state = State.new
       end
 
-      def to_s
-        chr = lambda do |value|
-          if value < 32 || value > 127
-            "{#{value}}"
-          else
-            value.chr
-          end
-        end
-        rv = ""
-        states = {start_state => 0}
-        to_visit = [start_state]
-        state_id = lambda do |state|
-          unless states.include?(state)
-            states[state] = states.values.max + 1
-            to_visit << state
-          end
-          states[state]
-        end
-        visit = lambda do |state|
-          accepts_s = state.accepts ? " *" : ""
-          rv += "#{state_id[state]}#{accepts_s}:\n"
-          state.transitions.each do |transition|
-            if transition.nil?
-              range_s = "nil"
-            else
-              range_s = chr[transition.code_point_range.first]
-              if transition.code_point_range.size > 1
-                range_s += "-" + chr[transition.code_point_range.last]
-              end
-            end
-            accepts_s = transition.destination.accepts ? " *" : ""
-            rv += "  #{range_s} => #{state_id[transition.destination]}#{accepts_s}\n"
-          end
-        end
-        while to_visit.size > 0
-          visit[to_visit[0]]
-          to_visit.slice!(0)
-        end
-        rv
-      end
-
       class << self
 
         def empty