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(Step-by-step execution)
Graph: , , , . Start DFS at . Visit : disc[0]=0. Visit : disc[1]=1. Visit : disc[2]=2. Back edge : low[2]=0. Backtrack: low[1]=0. Visit : disc[3]=3, low[3]=3. Backtrack: check low[3]=3 >= disc[1]=1, so is an articulation point.
Root has only child, so not an articulation point. Final articulation points: . Removing splits the graph into and .
