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+package FLAT;
+use FLAT::Regex;
+use FLAT::NFA;
+use FLAT::DFA;
+use Carp;
+
+use vars '$VERSION';
+$VERSION = 0.9.1;
+
+=head1 NAME
+
+FLAT - Formal Language & Automata Toolkit
+
+=head1 SYNOPSIS
+
+FLAT.pm is the base class of all regular language objects. For more
+information, see other POD pages.
+
+=head1 USAGE
+
+All regular language objects in FLAT implement the following methods.
+Specific regular language representations (regex, NFA, DFA) may implement
+additional methods that are outlined in the repsective POD pages.
+
+=cut
+
+## let subclasses implement a minimal set of closure properties.
+## they can override these with more efficient versions if they like.
+
+sub as_dfa {
+    $_[0]->as_nfa->as_dfa;
+}
+
+sub as_min_dfa {
+    $_[0]->as_dfa->as_min_dfa;
+}
+
+sub is_infinite {
+    ! $_[0]->is_finite;
+}
+
+sub star {
+    $_[0]->kleene
+}
+
+sub difference {
+    $_[0]->intersect( $_[1]->complement );
+}
+
+sub symdiff {
+    my $self = shift;
+    return $self if not @_;
+    my $next = shift()->symdiff(@_);
+    ( $self->difference($next) )->union( $next->difference($self) );
+}
+
+sub equals {
+    $_[0]->symdiff($_[1])->is_empty
+}
+
+sub is_subset_of {
+    $_[0]->difference($_[1])->is_empty
+}
+
+BEGIN {
+    for my $method (qw[ as_nfa as_regex union intersect complement concat
+                        kleene reverse is_empty is_finite ])
+    {
+        no strict 'refs';
+        *$method = sub {
+            my $pkg = ref $_[0] || $_[0];
+            carp "$pkg does not (yet) implement $method";
+        };
+    }
+}
+
+1;
+
+__END__
+
+=head2 Conversions Among Representations
+
+=over
+
+=item $lang-E<gt>as_nfa
+
+=item $lang-E<gt>as_dfa
+
+=item $lang-E<gt>as_min_dfa
+
+=item $lang-E<gt>as_regex
+
+Returns an equivalent regular language to $lang in the desired
+representation. Does not modify $lang (even if $lang is already in the
+desired representation).
+
+For more information on the specific algorithms used in these conversions,
+see the POD pages for a specific representation.
+
+=back
+
+=head2 Closure Properties
+
+=over
+
+=item $lang1-E<gt>union($lang2, $lang3, ... )
+
+=item $lang1-E<gt>intersect($lang2, $lang3, ... )
+
+=item $lang1-E<gt>concat($lang2, $lang3, ... )
+
+=item $lang1-E<gt>symdiff($lang2, $lang3, ... )
+
+Returns a regular language object that is the union, intersection,
+concatenation, or symmetric difference of $lang1 ... $langN, respectively.
+The return value will have the same representation (regex, NFA, or DFA) 
+as $lang1.
+
+=item $lang1-E<gt>difference($lang2)
+
+Returns a regular language object that is the set difference of $lang1 and
+$lang2. Equivalent to
+
+  $lang1->intersect($lang2->complement)
+
+The return value will have the same representation (regex, NFA, or DFA) 
+as $lang1.
+
+=item $lang-E<gt>kleene
+
+=item $lang-E<gt>star
+
+Returns a regular language object for the Kleene star of $lang. The return
+value will have the same representation (regex, NFA, or DFA) as $lang.
+
+=item $lang-E<gt>complement
+
+Returns a regular language object for the complement of $lang. The return
+value will have the same representation (regex, NFA, or DFA) as $lang.
+
+=item $lang-E<gt>reverse
+
+Returns a regular language object for the stringwise reversal of $lang.
+The return value will have the same representation (regex, NFA, or DFA)
+as $lang.
+
+=back
+
+=head2 Decision Properties
+
+=over
+
+=item $lang-E<gt>is_finite
+
+=item $lang-E<gt>is_infinite
+
+Returns a boolean value indicating whether $lang represents a
+finite/infinite language.
+
+=item $lang-E<gt>is_empty
+
+Returns a boolean value indicating whether $lang represents the empty
+language.
+
+=item $lang1-E<gt>equals($lang2)
+
+Returns a boolean value indicating whether $lang1 and $lang2 are
+representations of the same language.
+
+=item $lang1-E<gt>is_subset_of($lang2)
+
+Returns a boolean value indicating whether $lang1 is a subset of
+$lang2.
+
+=item $lang-E<gt>contains($string)
+
+Returns a boolean value indicating whether $string is in the language
+represented by $lang.
+
+=back
+
+=head1 AUTHORS & ACKNOWLEDGEMENTS
+
+FLAT is written by Mike Rosulek E<lt>mike at mikero dot comE<gt> and Brett 
+Estrade E<lt>estradb at gmail dot comE<gt>.
+
+The initial version (FLAT::Legacy) by Brett Estrade was work towards an MS 
+thesis at the University of Southern Mississippi.
+
+=head1 LICENSE
+
+This module is free software; you can redistribute it and/or modify it under
+the same terms as Perl itself.
+
+=head1 MORE INFO
+
+Please visit the Wiki at http://www.0x743.com/flat