0(1) element: null
1(2) element: PyMatchStatement
2(3,6) refutable pattern: 42
3(4) matched pattern: 42
4(5) element: PyExpressionStatement
5(9) READ ACCESS: y
6(7) WRITE ACCESS: x
7(8) element: PyExpressionStatement
8(9) READ ACCESS: y
9(10) element: PyExpressionStatement
10(11) READ ACCESS: z
11() element: null