meow :3

I'm pretty sure 6 is min mecha:
1 for the arm base, 1 for the input
2 for the bonder, which needs to be full access, because there are only single atoms at the beginning.
1 for rejection, this can be half access because it's possible to reach the other part with bonded silvers.
1 for output

I tried a couple different setups, but none get a smaller area than this.

Having a mecha of 6 should mean there aren't that many possibilities, but the last time I thought that, I was proven quite wrong.

meow meow meow meow :3