op.rb

class Fixnum
  def +@
    2
  end

  def -@ # !> method redefined; discarding old -@
    -2
  end

  def +(o) # !> method redefined; discarding old +
    3
  end

  def -(o) # !> method redefined; discarding old -
    -3
  end
end

0 - 1 # => -3
  - 1 # => -2
   -1 # => -1
   +1 # => 1
  + 1 # => 2
0 + 1 # => 3