User blog comment:CatIsFluffy/Ordinals in SKI/@comment-11227630-20180124000756

S(SKK)(S(SKK)(SKK))x = SKKx(S(SKK)(SKK)x) = SKKx(SKKx(SKKx)) = Kx(Kx)(Kx(Kx)(Kx(Kx))) = x(xx), so S(SKK)(S(SKK)(SKK)) is eta-equivalent to λx.x(xx), not λx.xxx