YES * Step 1: UnsatPaths YES + Considered Problem: Rules: 0. l0(A,B,C,D) -> l1(0,B,C,D) True (1,1) 1. l1(A,B,C,D) -> l2(A,B,0,0) [A >= 0 && B >= 1] (?,1) 2. l2(A,B,C,D) -> l2(A,B,1 + C,C + D) [D >= 0 (?,1) && C + D >= 0 && -1 + B + D >= 0 && A + D >= 0 && C >= 0 && -1 + B + C >= 0 && A + C >= 0 && -1 + B >= 0 && -1 + A + B >= 0 && A >= 0 && B >= 1 + C] 3. l2(A,B,C,D) -> l1(A + D,-1 + B,C,D) [D >= 0 (?,1) && C + D >= 0 && -1 + B + D >= 0 && A + D >= 0 && C >= 0 && -1 + B + C >= 0 && A + C >= 0 && -1 + B >= 0 && -1 + A + B >= 0 && A >= 0 && C >= B] Signature: {(l0,4);(l1,4);(l2,4)} Flow Graph: [0->{1},1->{2,3},2->{2,3},3->{1}] + Applied Processor: UnsatPaths + Details: We remove following edges from the transition graph: [(1,3)] * Step 2: Looptree YES + Considered Problem: Rules: 0. l0(A,B,C,D) -> l1(0,B,C,D) True (1,1) 1. l1(A,B,C,D) -> l2(A,B,0,0) [A >= 0 && B >= 1] (?,1) 2. l2(A,B,C,D) -> l2(A,B,1 + C,C + D) [D >= 0 (?,1) && C + D >= 0 && -1 + B + D >= 0 && A + D >= 0 && C >= 0 && -1 + B + C >= 0 && A + C >= 0 && -1 + B >= 0 && -1 + A + B >= 0 && A >= 0 && B >= 1 + C] 3. l2(A,B,C,D) -> l1(A + D,-1 + B,C,D) [D >= 0 (?,1) && C + D >= 0 && -1 + B + D >= 0 && A + D >= 0 && C >= 0 && -1 + B + C >= 0 && A + C >= 0 && -1 + B >= 0 && -1 + A + B >= 0 && A >= 0 && C >= B] Signature: {(l0,4);(l1,4);(l2,4)} Flow Graph: [0->{1},1->{2},2->{2,3},3->{1}] + Applied Processor: Looptree + Details: We construct a looptree: P: [0,1,2,3] | `- p:[1,3,2] c: [3] | `- p:[2] c: [2] YES