my %table = (
  recent => {'c:/autoexec.bat'=>undef, 'c:/frog.jpg'=>undef},
  text => {'c:/autoexec.bat'=>undef, 'c:/classnotes.txt'=>undef},
  biology => {'c:/classnotes.txt'=>undef, 'c:/frog.jpg'=>undef},
);
##</code><code>##

my @terms = ('recent', 'biology');
my @matches = keys %{  $table{  (shift @terms)  }   };
foreach my $term (@terms)
{
  @matches = grep { exists $table{$term}{$_} } @matches;
}
printf "Found %05d matches!\n", scalar @matches;