When I use NULL in a CWEB document, it is typeset as Λ (\Lambda) in the cweave output. Indeed, I see \let\NULL=\Lambda in cwebmac.tex. Why is this the default?

I was very puzzled when I first looked at the symbol--I realized that it meant NULL only because of the context, not by the symbol itself.

While I'm not really sure whether this question is good fit here, only results I could find on google with "NULL Lambda CWEB" was about AWS Lambda.

1 Answer 1


Knuth uses the convention that \Lambda stands for the null link (nil) in his series of books The Art of Computer Programming. In Volume 1, section 2.1 (the introduction of chapter 2 "Information Structures"), page 234, he writes:

...; we use the capital Greek letter Lambda to denote the null link, the link to no node.

Thus, he uses this convention since the 1960s.

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