Where do you see a minimum?while the minimum amount of space, the 100 square miles that *have* to be dedicated to the Capitol,
Where does it said that land must be retrocessed? Just because there was a retrocession of land, doesn't mean that land can't be turned into state instead. Maryland doesn't even want DC....and they can't because the territory would have to be returned to the states it originally belonged
https://en.m.wikipedia.org/wiki/Outline_of_Washington,_D.C.
In 1864 31 square miles of District of Columbia were returned to the state of Virginia due to retrocession. The remainder of the territory, in the event of shrinking DC, would go to Maryland.

