How can I remove from a STRING VARIABLE all characters that are not part of a predefined list? For example, the predefined list contains the characters 1, 2, 3, A, B, and C. If the STRING is "12A", it does not change; but if it is "14A", it will change to "1A" because "4" is not in the list. In short, I do not want to define the characters to delete but the characters to keep. Thanks