:{0, 1}4 → {0, 1}4. d(x) is obtained from x by removing the second bit and placing it at the end. for example, f(1011) = 1110. f: {0, 1}4 → {0, 1}4. f(x) is obtained from x by replacing the last bit with 1. for example, f(1000) = 1001. g: {0, 1}4 → {0, 1}3. g(x) is obtained from x by removing the first bit. for example, g(1000) = 000. (a) what is d-1(1001)? (b) which of the following functions is not well defined, f ο g or g ο f?