YES Problem: a(a(b(d(b(d(a(x1))))))) -> a(a(c(a(a(b(d(x1))))))) a(a(c(x1))) -> c(c(a(a(x1)))) c(c(c(x1))) -> b(d(c(b(d(x1))))) Proof: String Reversal Processor: a(d(b(d(b(a(a(x1))))))) -> d(b(a(a(c(a(a(x1))))))) c(a(a(x1))) -> a(a(c(c(x1)))) c(c(c(x1))) -> d(b(c(d(b(x1))))) Matrix Interpretation Processor: dim=3 interpretation: [1 0 0] [d](x0) = [0 0 0]x0 [0 1 1] , [1 0 0] [c](x0) = [0 1 0]x0 [0 0 0] , [1 0 1] [0] [a](x0) = [0 0 0]x0 + [1] [0 0 1] [0], [1 0 0] [b](x0) = [0 0 1]x0 [0 1 0] orientation: [1 0 3] [1] [1 0 2] [0] a(d(b(d(b(a(a(x1))))))) = [0 0 0]x1 + [1] >= [0 0 0]x1 + [0] = d(b(a(a(c(a(a(x1))))))) [0 0 1] [1] [0 0 0] [1] [1 0 2] [0] [1 0 0] [0] c(a(a(x1))) = [0 0 0]x1 + [1] >= [0 0 0]x1 + [1] = a(a(c(c(x1)))) [0 0 0] [0] [0 0 0] [0] [1 0 0] [1 0 0] c(c(c(x1))) = [0 1 0]x1 >= [0 0 0]x1 = d(b(c(d(b(x1))))) [0 0 0] [0 0 0] problem: c(a(a(x1))) -> a(a(c(c(x1)))) c(c(c(x1))) -> d(b(c(d(b(x1))))) String Reversal Processor: a(a(c(x1))) -> c(c(a(a(x1)))) c(c(c(x1))) -> b(d(c(b(d(x1))))) Bounds Processor: bound: 1 enrichment: match automaton: final states: {6,1} transitions: c0(4) -> 5* c0(5) -> 1* c0(8) -> 9* c1(31) -> 32* c1(13) -> 14* b0(7) -> 8* b0(10) -> 6* d1(29) -> 30* d1(14) -> 15* d1(11) -> 12* d1(32) -> 33* b1(12) -> 13* b1(15) -> 16* b1(33) -> 34* b1(30) -> 31* d0(2) -> 7* d0(9) -> 10* f40() -> 2* a0(2) -> 3* a0(3) -> 4* 16 -> 1* 4 -> 29* 1 -> 3,4 34 -> 5* 5 -> 11* problem: Qed