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