one well-known strategy for distinguishing smooth structures on closed 4-manifolds is to produce a knot $k$ in $s^3$ which is (smoothly) slice in one smooth filling $w$ of $s^3$ but not slice in some homeomorphic smooth filling $w’$. there are many techniques for distinguishing smooth structures on complicated closed 4-manifolds, but this strategy stands out for it’s potential to work for 4-manifolds $w$ with very little algebraic topology. however, this strategy had never actually been used in practice, even for complicated $w$. i’ll discuss joint work with manolescu and marengon which gives the first application of this strategy. i’ll also discuss joint work with manolescu which gives a systematic approach towards using this strategy to produce exotic definite closed 4-manifolds.