You are probably right about 2021, but I think it is very likely that when L5 does come, it will arrive suddenly and unexpectedly. The same as AlphaGo did. Yes,

You are probably right about 2021, but I think it is very likely that when L5 does come, it will arrive suddenly and unexpectedly. The same as AlphaGo did. Yes, I am aware that AlphaGo was the result of years of effort. Obviously there is an element of “how do you define ‘arrive’“ here.