Graph: , , , . Start DFS at . Discovery times: disc[1]=0, disc[2]=1, disc[3]=2, disc[4]=3. Low-link values: low[1]=0 (reaches itself), low[2]=0 (back edge reaches ), low[3]=0 (back edge ), low[4]=3 (no back edges, dead end).
Edge is a bridge because low[4]=3 > disc[2]=1. The subtree of cannot reach anything earlier than itself. Removing edge disconnects node from the rest.