=== List ===
Avalog supports variable number of arguments,
which can be used to represent lists.

For example:

  (do, copy(A)) :- (do, copy(A, ..)).
  (do, copy(B)) :- (do, copy(A, ..B)).
  (do, copy(a, b, c, d))

The pattern `..` ignores the tail.
The pattern `..B` puts the tail in a new list.

This generates the following pairs:

  (do, copy(a))
  (do, copy(b))
  (do, copy(c))
  (do, copy(d))