#!/usr/bin/perl -w

use strict;

my @chicago{   qw(tiger bob munch toy)    } = ();
my @wisconsin{ qw( tiger sara munch toy ) } = ();
my @rockford{  qw( tiger sara love toy )  } = ();


sub intersection {
    my ( $i, $sizei ) = ( 0, scalar keys %{ $_[0] });
    my ( $j, $sizej );

    for ( $j = 1; $j < @_; $j++ ) {
           $sizej = keys %{ $_[ $j ] };
           ( $i, $sizei ) = ( $j, $sizej ) if $sizej < $sizei;
    }

    my @intersection = keys %{ splice @_, $i, 1 };
    my $set;
    while ( $set = shift ) {
             @intersection = grep { exists $set->{ $_ } } @intersection;
    }

    my %intersection;
    @intersection{ @intersection } = ();

    return \%intersection;
}

my $newIntersection = &intersection( \%chicago, \%wisconsin, \%rockford );

print join(" ", keys %{ $newIntersection }), "\n";