sink: "{ S[] -> a[] }"
must_source: "{ T[] -> a[]; U[] -> a[] }"
may_source: "{ V[] -> a[] }"
schedule:
domain: "{ S[]; U[]; T[]; V[] }"
child:
sequence:
- filter: "{ U[]; T[]; V[] }"
child:
sequence:
- filter: "{ U[] }"
- filter: "{ V[]; T[] }"
- filter: "{ S[] }"