Two-Person Economy Redux

        Your income |                   x
                    |         x         x
                    |         x    x    x    x
                    |    x    x    x    x    x
                    |    x    x    x    x    x
                    ------------------------------------
                    |    y    y    y    y    y      Year
                    |    y    y    y    y    y
                    |         y    y    y    y
                    |         y         y
        My spending |                   y

• If one sector is running a surplus, at least one of other sectors must run a deficit

• Changes in sector balances sum to 0