Years ago calcyman built an unbounded binary counter, but the actual pattern has been lost -- or at least it's very inconvenient to get to, saved on a possibly defunct hard drive on an ancient PC in the back of a closet somewhere.)
It seems odd that we don't already have an infinite stable memory-tape mechanism that can be set up to do an unbounded binary count, out into empty space (i.e., O(log T) growth). So if someone can point out an existing mechanism that I've forgotten about, I'll be most grateful... as well as a little embarrassed, probably..
Otherwise, let's just go ahead and build a new binary counter with modern Life technology; we can probably improve quite a bit on the original.
What is the smallest TEST glider salvo, aimed at some elbow object, with the following properties?
- If there's an empty space adjacent to the elbow, the salvo produces Still Life S off to the side, plus a piece of junk in the salvo lanes that can be used to restore the elbow, and also a 180-degree return glider (traveling in the opposite direction from the salvo, on a lane that doesn't interfere with Still Life S).
- If Still Life S already exists off to the side, the salvo removes it as well as the elbow object, and sends back a return glider on a different lane. Again, gliders anywhere along this new lane must not affect Still Life S.
Other mechanisms that will be needed include
- CARRY: a salvo converting the leftover junk object into a standard elbow in a new location, diagonally farther away from the salvo source. The distance must be far enough away that the TEST salvo can be repeated without affecting copies of Still Life S, either one step farther or one step closer to the glider source from this position.
- RESET: a mechanism that places a new elbow object next to position zero on the diagonal tape.