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