struct Tensor{}
fn (t Tensor) [] (parts []SliceIndex) string {return ''}
fn    fn_contains_index_expr()  {
 arr := [1, 2, 3, 4,   5]
	t:=Tensor{}
    a := 1 in arr[ 0.. ]
_ := a
  _  := 1  in arr[ ..2  ]
      _ := 1 in arr[1..3]
   d :=  arr[2]
     _ := d
     _ := arr[2 ..]
 _ := arr[.. 2 ]
   _ := arr[ 1 .. 3]
   _ := t[1..3,  ..]
   _ := t [ 1,2]
}