formalizes of Move 4 — Only the asymmetry of the base case lets the mirroring end.
def reflect(x): if not x: # the necessary flaw return ["·"] # one branch refuses to mirror head, *tail = x return reflect(tail) + [head] # everything else folds back
reflect(["a", "b", "c"]) # ['·', 'c', 'b', 'a']