Programming while someone watches is more like… Forgetting absolutely everything about how to program and moving at a pace 50x slower than if I were alone.

add = (
    lambda f: (lambda g: f(lambda *h: g(g)(*h)))(
               lambda g: f(lambda *h: g(g)(*h))
    )
)((lambda _add: lambda a, b: _add(a ^ b, c << 1) if (c := a & b) else a ^ b))