Let $\gamma(G)$ and $\gamma_t(G)$ denote the domination number and the total domination number. respectively. of a graph $G$ with no isolated vertices. It is well-known that $\gamma_t(G) \leq 2\gamma(G)$. https://www.roneverhart.com/Corvette-Spark-Plugs-Set-NGK-Iridium-IX-1992-1995-C4/