Well, the terse notation is indeed to terse for me, and I'm not even sure what I'm trying to understand, but the explanation on the other hand is too long. Wha

Well, the terse notation is indeed to terse for me, and I'm not even sure what I'm trying to understand, but the explanation on the other hand is too long. What's the null element of the set of expressions? Is (\lambda x. ) not valid and applicable?