0(1) element: null
1(2) element: PyMatchStatement
2(3) WRITE ACCESS: x
3(4,7) READ ACCESS: x
4(5) element: PyStatementList. Condition: x > 0:true
5(6) element: PyExpressionStatement
6(7) READ ACCESS: y
7(8) element: PyExpressionStatement
8(9) READ ACCESS: z
9() element: null