[subroutine]

In keeping with the original authors description, the aliens can only see the opening move. I'm confused - how could they determine there are 64 fields (nb: I only know the very basics of chess)?

If they could view entire matches, it seems a trivial task to acquire a complete understanding of the underlying game, no?

[tiborsaas]

Oh sorry, I missed that part. But according to the rules of chess a random valid opening should cover all fields on the table so at least you'd know the layout. Pawns can move one or two fields.

Knowing only the first move would limit understanding heavily, that's true.