text: #import <Foundation/Foundation.h>
  /**
   * SIMLuhnValidator determines if a string of digits is a valid credit card number according to the Luhn algorithm
   */
  @interface SIMLuhnValidator : NSObject
  
  /**
   Validates a string of digits based on the Luhn algorithm.  If the string has non-digits, then it is immediately invalidated.
   @param cardNumberString should be a string of digits
   @return BOOL YES if cardNumberString is valid according to the Luhn algorithm
   */
  
  -(BOOL)luhnValidateString:(NSString *)cardNumberString;
  @end
  