0(1) element: null
1(2) element: PyMatchStatement
2(3) refutable pattern: [x] | x
3(4,6) refutable pattern: [x]
4(5,6) WRITE ACCESS: x
5(7) matched pattern: [x]
6(7,11) WRITE ACCESS: x
7(8) matched pattern: [x] | x
8(9) element: PyStatementList
9(10) element: PyExpressionStatement
10(12) READ ACCESS: y
11(12) ASSERTTYPE ACCESS: null
12(13) element: PyExpressionStatement
13(14) READ ACCESS: z
14() element: null