  What is the simplest smooth simply connected 4-manifold embedded in $CP^3$
homologous to a degree $d$ hypersurface $V_d$? A version of this question
associated with Thom asks if $V_d$ has the smallest $b_2$ among all such
manifolds. While this is true for degree at most $4$, we show that for all $d
\geq 5$, there is a manifold $M_d$ in this homology class with $b_2(M_d) <
b_2(V_d)$. This contrasts with the Kronheimer-Mrowka solution of the Thom
conjecture about surfaces in $CP^2$, and is similar to results of Freedman for
$2n$-manifolds in $CP^{n+1}$ with $n$ odd and greater than $1$.
