The first one multiplies x by 2, the second one is the inverse of the 3x+1 rule. Technically, it is not exactly the inverse of the Collatz function, but the conjecture is still true if and only if these two rules can generate every natural number (if we ignore the upper bound in the first rule).
Finally I created an instance model for the initial state and set up a state space. In the following video you can see how to use Henshin's state space explorer to generate the Collatz graph. Have fun.