fun findCriticalEdges ((E,G) : ugraph) : edges =
  let
    val n = Seq.length G
    val zs = Seq.tabulate (fn _=>0) n
    val V = Seq.tabulate (fn i=>i) n
    val X = STSeq.fromSeq (Seq.tabulate (fn _=>false) n)
    val S = (STSeq.fromSeq zs, STSeq.fromSeq zs,0,~1)

    fun visit (D,LO,t,u) v =
    let
      val D' = STSeq.update(D,(v,t))
      val LO' = STSeq.update(LO,(v,t))
    in (D',LO',t+1,v) end

    fun revisit (D,LO,t,u) v =
    let
      val LO' = STSeq.update(LO,(u,min(STSeq.nth D v,STSeq.nth LO u)))
    in (D,LO',t,v) end

    fun finish (D,LO,t,u) v =
    let
      val LO' = STSeq.update(LO,(u,min(STSeq.nth LO v, STSeq.nth LO u)))
    in (D,LO',t,v) end

    fun dfs g ((s,x,p),v) =
      if(p=v) then (s,x,p)
      else if(STSeq.nth x v) then ((revisit s v),x,p)
      else
        let
          val s' = visit s v
          val x' = STSeq.update (x,(v,true))
          val (s'',x'',p') = Seq.iterate (dfs g) (s',x',v) (Seq.nth g v)
        in
          ((finish s'' v),x'',p')
        end

    val ((D,LO,_,_),_,_) = Seq.iterate (dfs G) (S,X,~1) V
    fun crit(u,v) = (STSeq.nth D u) < (STSeq.nth LO v)
  in
    Seq.filter crit E
  end