1must_dependence: "{ }" 2may_dependence: "{ [S_1[] -> __pet_ref_2[]] -> [[S_2[] -> __pet_ref_4[]] -> a[]]; [S_1[] -> __pet_ref_1[]] -> [[S_2[] -> __pet_ref_4[]] -> a[]] }" 3must_no_source: "{ }" 4may_no_source: "{ }" 5