My reaction was initially to the idea that they needed to "remember the first spell." That seemed to me more about getting in the right frame of mind or mindset, than a "rule" of establishing links, more "repeat this mantra" than "to fly you must think of your happiest memory."
I stand by my quick description: "use a noncaster in a link." Haha, reminds me of that "one coin is not a nickel" type of silly riddles.
They could not possibly win. Every man knew this with certainty, and lo it was glorious.