function is_sedamo($sedamo)
{  // verifies the check digit of the sedamo address code
	$letters = array("A"=>0, "B"=>1, "C"=>2, "D"=>3, "E"=>4, "F"=>5, "G"=>6, "H"=>7, "J"=>8, "K"=>9, "L"=>10, "M"=>11, "P"=>12, "Q"=>13, "R"=>14, "T"=>15, "U"=>16, "W"=>17, "X"=>18, "Y"=>19); // 20 characters
	
	if  (strlen($sedamo) != 8) { return(false); }
		else {
		for($i=1, $sum=0; $i<8; $i++)
			{
				$sum = $sum  + $i * $letters[($sedamo[($i)])];
			} // for
		return (fmod($sum, 20) == $letters[($sedamo[0])]);
		} // if-else
} // is_sedamo