MAYBE

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

Proof:
 Open