$\Omega (n\log n)$ Lower Bounds on Length of Boolean Formulas
Michael J. Fischer, Albert R. Meyer, Michael Stewart Paterson · SIAM Journal on Computing · 1982
A property of Boolean functions of n variables is described and shown to imply lower bounds as large as $\Omega (n\log n)$ on the number of literals in any Boolean formula for any function with the property. Formulas over the full basis of binary operations $( \wedge , \oplus ,{\text{ etc.}})$ are considered. The lower bounds apply to all but a vanishing fraction of symmetric functions, in particular, to all threshold functions with sufficiently large threshold and to the “congruent to zero modulo k” function for $k > 2$. In the case $k = 4$, the bound is optimal.