At=Struct.new(:al, :bl, :a, :b) do
    def initialize
        super
       self.b ||= self.a
    end

    def +(other)
    At.new(
      self.al + other.al,
      self.bl + other.bl,
      self.a + other.a,
      self.b + other.b
      )
    end

    def -(other)
    At.new(
      self.al + other.al,
      self.bl + other.bl,
      self.a - other.a,
      self.b - other.b
    )
    end
    def *(other)
    At.new(
      self.a * other.al + other.a * self.al,
      self.b * other.bl + other.b * self.bl,
      self.a * other.a,
      self.b * other.b
    )
    end
    def /(other)
    At.new(
      ((self.a * other.bl + other.b * self.al) / (other.b**2)).round(2).inspect,
      ((self.b * other.al + other.a * self.bl) / (other.a**2)).round(2),
      (self.a / other.b).round(2),
      (self.b / other.a).round(2)
    )
    end
end