Graph Properties / Features

14. In a directed graph, a vertex $v_2$ is reachable from a vertex $v_1$ if there exists a directed path from $v_1$ to $v_2$.
    

    Vertex $3$ is reachable from vertex $1$, but vertex $4$ isn't reachable from any node. Miriam Briskman, CC BY-NC 4.0.

    \documentclass[border=1pt]{standalone}
    \usepackage{tikz}
    \usetikzlibrary{arrows.meta}
    
    \tikzset{
    vertex/.style={draw, circle, very thick, minimum size=1cm},
    edge/.style={very thick, -Triangle}
    }
    
    \begin{document}
    
    \begin{tikzpicture}
    
    \node[vertex] (1) at (0,0) {$1$};
    \node[vertex] (2) at (3,0) {$2$};
    \node[vertex] (3) at (6,0) {$3$};
    
    \node[vertex] (4) at (3,-2) {$4$};
    
    \draw[edge] (1) -- (2);
    \draw[edge] (2) -- (3);
    
    \end{tikzpicture}
    
    \end{document}