Complex sentence: The time variable t can be a "continuous" one (i.e. t\\ in\\ mathbb) or a discrete one (i.e. t\\ in\\ mathbb): in the latter case the time variable is usually indicated as k.
Split into simpler sentences: The time variable t can be a "continuous" (e.g., t\\ in\\ mathbb) or discrete (e.g., t\\ in\\ mathbb). In the latter case, the time variable is usually indicated as k.