                                              alt="V"/> is a finite set of
                        nodes, <img class="math" src="../_images/math/d0caa3aa5a97d841c0f868222d3da555d5cad643.png"
                                    alt="T \subseteq\mathbb{R}"/> a time interval , <img class="math"
                                                                                         src="../_images/math/69e9d94b4777dfcbb3400d3244578b6c83d482a6.png"
                                                               