0(1) element: null
1(2) element: PyMatchStatement
2(3,16) refutable pattern: 1 | (2 | 3)
3(4,5) refutable pattern: 1
4(14) matched pattern: 1
5(6,16) refutable pattern: (2 | 3)
6(7,16) refutable pattern: 2 | 3
7(8,9) refutable pattern: 2
8(14) matched pattern: 2
9(10,16) refutable pattern: 3
10(11) matched pattern: 3
11(12) matched pattern: 2 | 3
12(13) matched pattern: (2 | 3)
13(14) matched pattern: 1 | (2 | 3)
14(15) element: PyExpressionStatement
15(16) READ ACCESS: x
16(17) element: PyExpressionStatement
17(18) READ ACCESS: y
18() element: null