method
    
    -
  -(a)
  public
  Returns the difference of this value and a. subtracted.
Examples:
r = Rational(3,4) # -> Rational(3,4) r - 1 # -> Rational(-1,4) r - 0.5 # -> 0.25
  -(a)
  public
  Returns the difference of this value and a. subtracted.
Examples:
r = Rational(3,4) # -> Rational(3,4) r - 1 # -> Rational(-1,4) r - 0.5 # -> 0.25