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