Effect of predomination and vertex removal on the game total domination number of a graph

The game total domination number, ${\gamma_{g}^{t}}$, was introduced by Henning et al.\ in 2015. In this paper we study the effect of vertex predomination on the game total domination number. We prove that ${\gamma_{g}^{t}}(G|v) \geq {\gamma_{g}^{t}}(G) - 2$ holds for all vertices $v$ of a graph $G$ and present infinite families attaining the equality. To achieve this, some new variations of the total domination game are introduced. The effect of vertex removal is also studied. We show that ${\gamma_{g}^{t}}(G) \leq {\gamma_{g}^{t}}(G-v) + 4$ and ${\gamma_{g}^{t}}'(G) \leq {\gamma_{g}^{t}}'(G-v) + 4$.