- a minimal room made of concrete walls, having one door and one window
- a recurse center, plus the opening of one more window
- the union of two recurse centres horizontally, by a tight wall-wall juxtaposition of the two of them, with the removal of one of their walls, and the opening of a door in the remaining one, if necessary
- a similar vertical union, with the addition of a stairwell
- the union of two recurse centres by the addition of an
external hallway, and the necessary doors.
- a few additional cases that can be neglected for the purposes of this paper
Unfortunately one problem with the recurse center's concrete rooms is that they were only architected to be able to handle immutable people, looking outside is strictly forbidden, and when you leave a room, it collapses.
It doesn't collapse in any way that you care about, though.
What is interesting is the possibility of tail recursing, but over a regular stack that is continuously abandoned. So the foundation and lower floors disappear, yet the recurse centre grows ever higher into the sky.
- a minimal room made of concrete walls, having one door and one window
- a recurse center, plus the opening of one more window
- the union of two recurse centres horizontally, by a tight wall-wall juxtaposition of the two of them, with the removal of one of their walls, and the opening of a door in the remaining one, if necessary
- a similar vertical union, with the addition of a stairwell
- the union of two recurse centres by the addition of an external hallway, and the necessary doors.
- a few additional cases that can be neglected for the purposes of this paper