But cons operates sequentially. I thought the point about merge is that it's not sequential?
{α, β}
Both α and β can be either some atomic unit, eg a word or a morpheme, or the previous output of Merge (a tree).
This is their first example as rendered as cons:
(cons I (cons drink wine))
As merge:
{ I, { drink, wine } }
As a tree:
Edit: I can't get the tree to look even remotely correct in HN formatting, but you get the idea. It's in the article.
>> [Merge] applies to discrete units of language (words or their parts). It combines these, not sequentially, but hierarchically.
Or the paragraph at the start where human language abilities are contrasted to bonobos' and chimpanzees' and deep learning models' sequential processing; etc.
My knowledge of Lisp is rusty, but as far as I remember it cons is a list operator that joins the head to the tail of a list (like the "|" in Prolog). So it imposes an order - on a sequence. Apologies if I misremember this.
The author is just trying to say that Merge is doing the same thing we're talking about cons doing to S-expressions to a tree and noting that it creates hierarchy. Eg a new Merge says I've created a new top-level node that is a parent for the two inputs. A second Merge says I've made the first input c-command both inputs of my first Merge and created a new top-level node.