sub binary_search {
	my ($aref, $find) = @_;
	my  $mid = int $#$aref / 2;

	return 0 unless $#$aref;
	return 1 if $find == $aref->[$mid];

	binary_search(
		$find < $aref->[$mid]
		? [ @$aref[     0 .. --$mid ] ]
		: [ @$aref[++$mid .. $#$aref] ]
		, $find
	);
}