I have an array 

```
$arr = [20,22,29,40,67,35,98,200,205,220];

```

In this we subtract 1st value from second,second from third, third from fourth value and so on.
After subtracting this way we get new values. These new values should follow the same procedure until there 
remain single value at the end. First time subtracting array values is simple but new values subtraction looks
difficult for me. Thanks.

I expect the output 

```
2, 7, 11, 27, -32, 63, 102, 5, 15
5, 4, 16, -59, 95, 39, -97, 10
-1, 12, -75, 154, -56, -136, 107
13, -87, 229, -210, -80, 243,
-100, 316, -439, 130, 323
416, -755, 569, 193
-1171, 1324, -376
2495, -1700
-4195

```