Function A($)

	
	dim $i, $x, $b, $l
	$l = len($)

	if $l = 15 or $l = 16
		redim $b[$l-1]
		for $i = 0 to $l-1
			$b[$i] = substr($,$i+1,1)
		next

		for $i = $l-2 to 0 step -2
			$x = 2*$b[$i]
			$b[$i] = iif($x>9,0+left($x,1) + right($x,1),$x)
		next

		$i = execute("$X="+join($b,'+'))
			
		if right($x,1) = 0
			$B = left($,1)
			if $b = 3
				if $l <> 15
					$b = 0
				endif
			else
				if instr('456',$b)
					if $l <> 16
						$b = 0
					endif	
				else
					$b = 0
				endif
			endif
		else
			$b = 0
		endif
	else
		$b = 0
	endif
	$a = $b


Endfunction

dim ... ,$b
...
    while $
        $b = ~$b
        $c = (2+$b) * right($,1)
        ....

function a($)
    dim $b, $c, $d
    $b = 0^$
    while $
        $c = (($b-($^) & 1)+1) * right($,1)
        $d = $d + $c-9*($c>9)
        $a = ($d mod 10 =) * ($>2&$<7&$b+($<4)=16) * $
        $ = left($,~)
endfunction

Function A($b)
Dim $t,$,$x

For $t=0 to 99
 $=Right($b,1)
 $x=$t mod 2*((4<$)+$)+$+$x
 $b=Left($b,~)
 If $
  $a=($t=15-(3=$) & 2<$ & 7>$ & $x mod 10=)*$
EndFunction

Function A($)
  Dim $D,$F,$I,$S			; Digit, Flag, ID, Sum
  $A=0					; default return
  $D=Len($)				; CC # length
  $I=Left($,1)	;			; CC Issuer ID
  If ($D=15&$I=3)|$D=16&$I>3&$I<7	; verify ID/# Digits
    While $				; while digits
      $D=(1+$F)*Right($,1)		; Get digit and optionally double
      $S=$S+IIf($D>9,$D-9,$D)		; sum digit
      $F=$F^1				; flip odd/even flag
      $=Left($,~)			; trim string
    Loop
  ; common code
    If $S Mod 10 = 0			; if CC is valid
      $A=$I				; return issuer code
EndFunction

function a($)
    dim $b, $c, $d, $e
    $e = $^0
    while $
        $b = ~$b
        $d = (2+$b) * right($,1)
        $c = $c + $d-9*($d>9)
        $a = ($c mod 10 =) * (($e=15&$=3)|$e=16&$>3&$<7) * $
        $ = left($,~)
endfunction

function a($)
    dim $b, $d
    $b = 0^$
    while $
        $a = (($b-($^) & 1)+1) * right($,1)
        $d = $d + $a-9*($a>9)
        $a = ($d mod 10 =) * ($>2&$<7&$b+($<4)=16) * $
        $ = left($,~)
endfunction

function a($)
    dim $b, $c, $e
    $e = $^0
    while $
        $b = ~$b
        $a = (2+$b) * right($,1)
        $c = $c + $a-9*($a>9)
        $a = ($c mod 10 =) * ($>2&$<7&$e+($<4)=16) * $
        $ = left($,~)
endfunction

Function A($b)
Dim $t,$,$x

For $t=0 to 99
 $=0+Right($b,1)
 $x=1 & $t *($/5+$)+$+$x
 $b=Left($b,~)
 If $
  $a=(2<$ & 7>$ & $t=14+$/4 & $x mod 10=)*$
EndFunction