Function A($)	
	$a = $^0
	dim $i, $x, $b[$a-1],$s
	
		for $i = $a-1 to 0 step -1
			$x = substr($,$i+1,1)
			if $s
				;$x = 2*$x
				;$x = $x-9*($x>9)
				$x = 2*$x+(4<$x) ; above lines combined
			endif
			$b[$i] = $x
			$s=$s^1
		next

		$i = execute("$X="+join($b,'+'))

		$a = ($>3 & $<7 & $a=16-($<4) & $x mod 10=)*left($,1)
Endfunction