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