0(1) element: null
1(2) element: PyMatchStatement
2(3,14) refutable pattern: 1
3(4) matched pattern: 1
4(5) element: PyStatementList
5(6) element: PyMatchStatement
6(7,11) refutable pattern: 11
7(8) matched pattern: 11
8(9) element: PyStatementList
9(10) element: PyExpressionStatement
10(12) READ ACCESS: y11
11(12) ASSERTTYPE ACCESS: null
12(13) element: PyExpressionStatement
13(20) READ ACCESS: y1
14(15,19) refutable pattern: 2
15(16) matched pattern: 2
16(17) element: PyStatementList
17(18) element: PyExpressionStatement
18(20) READ ACCESS: y2
19(20) ASSERTTYPE ACCESS: null
20(21) element: PyExpressionStatement
21(22) READ ACCESS: z
22() element: null