var expr = (
  from c in customers
    from o in c.Orders
      join p in products on o.IdProduct equals p.IdProduct
  where c.Country == Countries.Italy
  select p)
  .Intersect(
  from c in customers
    from o in c.Orders
      join p in products on o.IdProduct equals p.IdProduct
  where c.Country == Countries.USA
  select p);
