Let M be a set with |M| = n element in N. Show with complete induction that the number of all subsets with uneven absolute value from M is $2^{n-1}$. 

My beginning of the induction is |M| = 1 with M = {m1} so the subsets are {m1} and the null-set and {m1} is the only subset with uneven absolute value. I do not know how to continue.