# On monotone circuits with local oracles and clique lower bounds

## TL;DR

This paper studies the complexity of monotone circuits with local oracles, revealing phase transitions and bounds in separating specific graph classes, extending classical clique lower bounds.

## Contribution

It introduces new bounds and phase transition phenomena for monotone circuits with local oracles, extending classical clique lower bounds and analyzing their behavior.

## Key findings

- Size of circuits separating triangles and bipartite graphs exhibits phase transitions based on locality parameter.
- Monotone circuit size for separating k-cliques and (k-1)-partite graphs is n^{Θ(√k)} under certain conditions.
- Extends and matches previous exponential lower bounds on monotone circuit complexity for k-cliques.

## Abstract

We investigate monotone circuits with local oracles [K., 2016], i.e., circuits containing additional inputs $y_i = y_i(\vec{x})$ that can perform unstructured computations on the input string $\vec{x}$. Let $\mu \in [0,1]$ be the locality of the circuit, a parameter that bounds the combined strength of the oracle functions $y_i(\vec{x})$, and $U_{n,k}, V_{n,k} \subseteq \{0,1\}^m$ be the set of $k$-cliques and the set of complete $(k-1)$-partite graphs, respectively (similarly to [Razborov, 1985]). Our results can be informally stated as follows. 1. For an appropriate extension of depth-$2$ monotone circuits with local oracles, we show that the size of the smallest circuits separating $U_{n,3}$ (triangles) and $V_{n,3}$ (complete bipartite graphs) undergoes two phase transitions according to $\mu$. 2. For $5 \leq k(n) \leq n^{1/4}$, arbitrary depth, and $\mu \leq 1/50$, we prove that the monotone circuit size complexity of separating the sets $U_{n,k}$ and $V_{n,k}$ is $n^{\Theta(\sqrt{k})}$, under a certain restrictive assumption on the local oracle gates. The second result, which concerns monotone circuits with restricted oracles, extends and provides a matching upper bound for the exponential lower bounds on the monotone circuit size complexity of $k$-clique obtained by Alon and Boppana (1987).