the game — spot the difference, where sometimes there isn't one

each level is two doors; ask the probes your seat hears, one fuel each, and either name the probe that parts them or say they are alike at this seat. after alike you may widen, one fuel, and read what the face could not. in a ticking level the world moves on its own and you watch the face: tick, one fuel each, and call whether the doors have parted or never will.

every door, level, seat, tick, and mirror below is read from assays/game.lean; the engine is the_window_agrees_or_names_the_gap, the tick is the_tick_hears_the_secret_only_as_a_residue, the mirror is the_yield_fixes_the_agreed.