LuhnDoubleEven is the middle part of the Luhn set. It doesn't really do anything useful as a stand alone function but it is essential to the workings of the Luhn function.
LuhnDoubleEven (makeEven)
/*
A component of the Luhn function.
Take the number string supplied by Luhn and double every even position character of the original number.
Adding 0 to the front of odd length number strings adjusted the original number for this to work.
*/
If ( Length ( makeEven ) > 1 ; 2 * Middle(makeEven ; 1; 1) & Middle(makeEven ; 2; 1) & LuhnDoubleEven ( Right ( makeEven; Length ( makeEven ) - 2 ) )
; "" )