0(1) element: null
1(2) element: PyMatchStatement
2(3,9) refutable pattern: 1
3(4) matched pattern: 1
4(5) element: PyMatchStatement
5(6,13) refutable pattern: 11
6(7) matched pattern: 11
7(8) element: PyExpressionStatement
8(13) READ ACCESS: y11
9(10,13) refutable pattern: 2
10(11) matched pattern: 2
11(12) element: PyExpressionStatement
12(13) READ ACCESS: y2
13(14) element: PyExpressionStatement
14(15) READ ACCESS: z
15() element: null