Multiple "use": multiple module names allowed after "use". For instance:

  use int.Int, set.Fset, ref.Ref
  (as updated in the pigeonhole.mlw file)

Any module name can be followed by a "as M" clause, but only a single "import"
is allowed. For instance:

  use import int.Int as I, map.Map as M

imports both Int and Map. To import Int but not Map, one would have to write

  use import int.Int as I
  use map.Map as M