Graphs with large girth and chromatic number are hard for Nullstellensatz

We study the computational efficiency of approaches, based on Hilbert’s Nullstellensatz, which use systems of linear equations for detecting non-colorability of graphs having large girth and chromatic number. We show that for every non-$k$-colorable graph with $n$ vertices and girth $g>4k$, the algorithm is required to solve systems of size at least $n^{\mathrm{\Omega }(g)}$ in order to detect its non-$k$-colorability.