# For example, finding all 2001 or newer Chevys
my %temp_hash = reverse %makes;         # gives the id for each make
my $make_id = $temp_hash{'Chevrolet');  # get the id for Chevy

my %make_set = map { $_=>1 } @{$makes_idx{$make_id}};  # set of cars that are Chevys

# search above for 2001 or newer models
my @temp_years = grep { $_ >= 2001 } keys %years_idx;
my @result_ids = grep { exists $make_set{$_} } @years_idx{@temp_years};