If G is a solvable group, we take Δ(G) to be the character degree graph for G with primes as vertices. We prove that if Δ(G) is a square, then G must be a direct product. © 2011 Elsevier Inc.
Lewis, M. L., & Meng, Q. (2012). Square character degree graphs yield direct products. Journal of Algebra, 349(1), 185–200. https://doi.org/10.1016/j.jalgebra.2011.09.016