How to solve this puzzle of Martin Gardner? Martin Gardner mentioned the following &quot;chess&quot; problem in his column, Mathematical Games, for Scientific American (he got it from Smullyan, who learned about it from a high school math teacher):

... Assume that a game is played with the new rule that a knight can on a single turn move twice. It is not clear if this more powerful knight move is an advantage to the first or second player. The first player, White, offers to play the game without his queen. How can he be sure to win?

After thinking a bit, I could not make progress, so I look at the solution:

 White jumps queen's knight forward twice. Checkmate!

That's all it says. How is this a checkmate? I must be missing something.
According to the FIDE Laws of Chess:

1.4 The objective of each player is to place the opponent’s king ‘under attack’ in such a way that the opponent has no legal move.
1.4.1 The player who achieves this goal is said to have ‘checkmated’ the opponent’s king and to have won the game

That means that if white has a knight which is 2 normal knight moves away from the opponent's king then the opponent's king is in check, under attack.
Then consider white starting the game like this:
[fen &quot;&quot;]

1. Nc3 null 2. Nb5

Then you can see the black king is in check. On the knight's next move it can go Nb5-d6-e8. But there is no way for black to get out of check. Hence it is checkmate.