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

    def -@
        At.new(al, bl, -a, -b)
    end

    def positive?
        if self.a >= 0 && self.b >= 0
            return true
        end
    end

    def negative?
        if self.a < 0 && self.b<0
            return true
        end
    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)
        if [self, other].all?(&:positive?)
            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
            )
        elsif [self, other].all?(&:negative?)
            -self * -other
        elsif self.negative? && other.positive?
            -(-self * other)
         elsif self.positive? && other.negative?
            -(self * -other)
        end
    end

    def /(other)
    if [self, other].all?(&:positive?)
        At.new(
            ((self.a * other.bl + other.b * self.al) / (other.b**2)).round(2),
            ((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)
        )
    elsif [self, other].all?(&:negative?)
            -self / -other
    elsif self.negative? && other.positive?
            -(-self / other)
    elsif self.positive? && other.negative?
            -(self / -other)
    end
    end
end