anchor.diff:      let predicate = buildExpr<unit, bool> @"4 /?\ (1,2,3)" 
       let result = predicate ()
       Assert.False(result)
  +
  +[<Fact>]
  +let ``hasintersection operator should consider null to be the empty set`` () =
  +    let predicate = buildExpr<unit, bool> @"null /?\ (1,2,3)" 
  +    let result = predicate ()
  +    Assert.False(result)
  +    let predicate = buildExpr<unit, bool> @"(1,2,3) /?\ null" 
  +    let result = predicate ()
  +    Assert.False(result)
  +    let predicate = buildExpr<unit, bool> @"null /?\ null" 
  +    let result = predicate ()
  +    Assert.False(result)
  +
   
   //
   // Wish List / Ideas
  
positive.code:     Assert.True(result)
  
  [<Fact>]
  let ``hasintersection operator should show if tuples have intersection`` () =
      let predicate = buildExpr<unit, bool> @"(2,3,4) /?\ (3,4,5)" 
      let result = predicate ()
  
negative.code:     Assert.True(result)
  
  [<Fact>]
  let ``null should act as identity for the union operator`` () =
      let predstr = @"null \/ (1,2,3) = (1,2,3)"
      let predicate = buildExpr<unit, bool> predstr
      let result = predicate ()
      Assert.True(result)
      let predstr = @"(1,2,3) \/ null = (1,2,3)"
      let predicate = buildExpr<unit, bool> predstr
      let result = predicate ()
      Assert.True(result)
  
  [<Fact>]
  let ``intersection operator should find the intersection of tuples`` () =
      let predicate = buildExpr<unit, bool> @"(2,3,4) /\ (3,4,5) = (3,4)" 
      let result = predicate ()
  