YES Problem: a(a(x1)) -> b(b(b(x1))) b(b(x1)) -> c(c(c(x1))) c(c(x1)) -> d(d(d(x1))) b(x1) -> d(d(x1)) c(d(d(x1))) -> a(x1) Proof: Matrix Interpretation Processor: dim=1 interpretation: [b](x0) = x0 + 9, [d](x0) = x0 + 4, [a](x0) = x0 + 14, [c](x0) = x0 + 6 orientation: a(a(x1)) = x1 + 28 >= x1 + 27 = b(b(b(x1))) b(b(x1)) = x1 + 18 >= x1 + 18 = c(c(c(x1))) c(c(x1)) = x1 + 12 >= x1 + 12 = d(d(d(x1))) b(x1) = x1 + 9 >= x1 + 8 = d(d(x1)) c(d(d(x1))) = x1 + 14 >= x1 + 14 = a(x1) problem: b(b(x1)) -> c(c(c(x1))) c(c(x1)) -> d(d(d(x1))) c(d(d(x1))) -> a(x1) String Reversal Processor: b(b(x1)) -> c(c(c(x1))) c(c(x1)) -> d(d(d(x1))) d(d(c(x1))) -> a(x1) Bounds Processor: bound: 2 enrichment: match automaton: final states: {5} transitions: d0(5) -> 5* a1(22) -> 23* a1(52) -> 53* a0(5) -> 5* d2(45) -> 46* d2(24) -> 25* d2(40) -> 41* d2(41) -> 42* d2(26) -> 27* d2(44) -> 45* d2(46) -> 47* d2(42) -> 43* d2(25) -> 26* c0(5) -> 5* b0(5) -> 5* d1(16) -> 17* d1(15) -> 16* d1(34) -> 35* d1(14) -> 15* a2(68) -> 69* a2(80) -> 81* a2(74) -> 75* c1(12) -> 13* c1(10) -> 11* c1(11) -> 12* 27 -> 11* 43 -> 13,5 47 -> 12* 17 -> 11,5 35 -> 15* 69 -> 46,16 12 -> 68,52,34,24 11 -> 80,40 53 -> 45,5,14,10,22,15 75 -> 42* 13 -> 5* 5 -> 22,14,10 10 -> 74,44 81 -> 16,26 23 -> 46,45,16,15,5 problem: Qed