code: public void setDivisor(int radix, short exponent) {
          divisor = NFRule.power(radix, exponent);
  
          if (divisor == 0) {
              throw new IllegalStateException("Substitution with divisor 0");
          }
      }
docs: Sets the substitution's divisor based on the values passed in.
  @param radix The radix of the divisor.
  @param exponent The exponent of the divisor.