MAYBE

Problem:
 0(0(1(x1))) -> 0(2(3(0(1(x1)))))
 0(0(1(x1))) -> 0(4(0(5(4(1(x1))))))
 0(0(1(x1))) -> 2(1(0(0(3(4(x1))))))
 0(0(1(x1))) -> 4(0(5(4(0(1(x1))))))
 0(1(0(x1))) -> 0(0(2(1(2(x1)))))
 0(1(0(x1))) -> 1(0(0(5(4(x1)))))
 0(1(0(x1))) -> 0(0(2(5(4(1(x1))))))
 0(1(1(x1))) -> 1(0(3(4(1(x1)))))
 0(1(1(x1))) -> 5(0(3(4(1(1(x1))))))
 5(0(1(x1))) -> 0(5(4(1(x1))))
 5(0(1(x1))) -> 2(5(4(0(1(x1)))))
 5(0(1(x1))) -> 5(0(2(1(2(x1)))))
 5(0(1(x1))) -> 0(1(4(5(4(4(x1))))))
 5(0(1(x1))) -> 0(5(4(1(4(4(x1))))))
 5(0(1(x1))) -> 5(0(4(3(0(1(x1))))))
 5(1(0(x1))) -> 5(0(2(2(1(x1)))))
 5(1(0(x1))) -> 5(0(5(4(1(x1)))))
 5(1(0(x1))) -> 0(5(0(2(2(1(x1))))))
 5(1(0(x1))) -> 1(4(0(5(2(3(x1))))))
 5(1(0(x1))) -> 1(5(0(4(4(2(x1))))))
 5(1(0(x1))) -> 4(4(1(0(4(5(x1))))))
 5(1(1(x1))) -> 1(1(5(4(x1))))
 5(1(1(x1))) -> 5(4(1(1(x1))))
 5(1(1(x1))) -> 1(5(3(4(1(x1)))))
 5(1(1(x1))) -> 1(1(4(5(4(4(x1))))))
 5(1(1(x1))) -> 3(5(2(3(1(1(x1))))))
 5(1(1(x1))) -> 4(1(2(1(5(4(x1))))))
 0(1(3(0(x1)))) -> 0(2(0(2(1(3(x1))))))
 0(1(5(0(x1)))) -> 0(0(5(4(1(5(x1))))))
 0(1(5(0(x1)))) -> 0(5(4(2(1(0(x1))))))
 0(3(0(1(x1)))) -> 0(0(4(1(3(0(x1))))))
 0(3(1(0(x1)))) -> 0(0(2(3(1(x1)))))
 0(3(1(1(x1)))) -> 5(1(1(0(3(4(x1))))))
 5(0(1(0(x1)))) -> 5(0(0(4(1(3(x1))))))
 5(1(2(0(x1)))) -> 1(4(0(5(4(2(x1))))))
 5(1(2(0(x1)))) -> 5(0(4(2(2(1(x1))))))
 5(1(4(0(x1)))) -> 1(5(4(0(2(3(x1))))))
 5(1(4(0(x1)))) -> 4(5(2(1(3(0(x1))))))
 5(1(5(1(x1)))) -> 5(4(1(5(1(x1)))))
 5(3(0(1(x1)))) -> 0(1(5(2(3(x1)))))
 5(3(1(0(x1)))) -> 1(4(3(5(0(x1)))))
 5(3(1(0(x1)))) -> 1(5(0(4(3(x1)))))
 5(3(1(0(x1)))) -> 5(4(3(1(0(x1)))))
 5(3(1(0(x1)))) -> 1(3(0(4(3(5(x1))))))
 5(3(1(1(x1)))) -> 1(1(5(3(3(4(x1))))))
 0(1(2(5(0(x1))))) -> 1(5(4(0(2(0(x1))))))
 0(1(4(2(0(x1))))) -> 1(0(4(2(3(0(x1))))))
 1(4(5(1(0(x1))))) -> 5(4(2(1(1(0(x1))))))
 5(0(1(4(0(x1))))) -> 1(4(5(4(0(0(x1))))))
 5(5(1(0(0(x1))))) -> 5(5(0(4(1(0(x1))))))

Proof:
 Open