code: public Decimal minus(Decimal subtrahend) {
          if ((this == NaN) || (subtrahend == NaN)) {
              return NaN;
          }
          return new Decimal(delegate.subtract(subtrahend.delegate, MATH_CONTEXT));
      }
docs: Returns a {@code Decimal} whose value is {@code (this - augend)},
  with rounding according to the context settings.
  @param subtrahend value to be subtracted from this {@code Decimal}.
  @return {@code this - subtrahend}, rounded as necessary
  @see BigDecimal#subtract(java.math.BigDecimal, java.math.MathContext)