must_dependence: "{  }"
may_dependence: "{ [S_1[] -> __pet_ref_2[]] -> [[S_2[] -> __pet_ref_4[]] -> a[]]; [S_1[] -> __pet_ref_1[]] -> [[S_2[] -> __pet_ref_4[]] -> a[]] }"
must_no_source: "{  }"
may_no_source: "{  }"