We introduce a general procedure called 'reverse engineering' that can be used to construct infinite families of smooth 4-manifolds in a given homeomorphism type. As one of the applications of this technique, we produce an infinite family of pairwise nondiffeomorphic 4-manifolds homeomorphic to ‫ސރ‬ 2 # ‫ސރ3‬ 2 .

We construct infinitely many distinct irreducible smooth structures on $n(S^2\,\times\,S^2)$, the connected sum of n copies of $S^2\,\times\,S^2$, for every odd integer $n\geq 27$.