human: Given a node-centered hypergraph: <hypergraph>, where nodes represent papers and hyperedges represent sets of papers co-cited by a source paper.

Details of the hypergraph:
Center node: "on the tree augmentation problem"
  Abstract: In the Tree Augmentation problem we are given a tree $T=(V,F)$ and a set $E \subseteq V \times V$ of edges with positive integer costs $\{c_e:e \in E\}$. The goal is to augment $T$ by a minimum cost edge set $J \subseteq E$ such that $T \cup J$ is $2$-edge-connected. We obtain the following results. #R##N#Recently, Adjiashvili [SODA 17] introduced a novel LP for the problem and used it to break the $2$-approximation barrier for instances when the maximum cost $M$ of an edge in $E$ is bounded by a constant; his algorithm computes a $1.96418+\epsilon$ approximate solution in time $n^{{(M/\epsilon^2)}^{O(1)}}$. Using a simpler LP, we achieve ratio $\frac{12}{7}+\epsilon$ in time $2^{O(M/\epsilon^2)} poly(n)$.This gives ratio better than $2$ for logarithmic costs, and not only for constant costs. #R##N#One of the oldest open questions for the problem is whether for unit costs (when $M=1$) the standard LP-relaxation, so called Cut-LP, has integrality gap less than $2$. We resolve this open question by proving that for unit costs the integrality gap of the Cut-LP is at most $28/15=2-2/15$. In addition, we will prove that another natural LP-relaxation, that is much simpler than the ones in previous work, has integrality gap at most $7/4$.

Connected through hyperedge HE-1 (induced by source paper "2 node connectivity network design"):
  with members:
    - "breaching the 2 approximation barrier for connectivity augmentation a reduction to steiner tree"
    - "approximating k connected m dominating sets"
    - "improved approximation for tree augmentation saving by rewiring"
    - "approximation algorithm for minimum weight fault tolerant virtual backbone in unit disk graphs"
    - "a simplified 1 5 approximation algorithm for augmenting edge connectivity of a graph from 1 to 2"
    - "improved approximation algorithms for budgeted node weighted steiner problems"
    - "nearly tight low stretch spanning trees"
    - "lower stretch spanning trees"

Connected through hyperedge HE-2 (induced by source paper "flexible graph connectivity approximating network design problems between 1 and 2 connectivity"):
  with members:
    - "5 4 approximation of minimum 2 edge connected spanning subgraph"
    - "how to secure matchings against edge failures"
    - "improved approximation for tree augmentation saving by rewiring"
    - "robust assignments via ear decompositions and randomized rounding"
    - "a simplified 1 5 approximation algorithm for augmenting edge connectivity of a graph from 1 to 2"
    - "analytical approach to parallel repetition"
    - "greedy facility location algorithms analyzed using dual fitting with factor revealing lp"

Connected through hyperedge HE-3 (induced by source paper "breaching the 2 approximation barrier for connectivity augmentation a reduction to steiner tree"):
  with members:
    - "improved approximation for tree augmentation saving by rewiring"
    - "a simplified 1 5 approximation algorithm for augmenting edge connectivity of a graph from 1 to 2"
    - "approximating unweighted tree augmentation via lift and project part ii"

Connected through hyperedge HE-4 (induced by source paper "improved approximation for tree augmentation saving by rewiring"):
  with members:
    - "a frac 3 2 approximation algorithm for tree augmentation via chvatal gomory cuts"
    - "a simplified 1 5 approximation algorithm for augmenting edge connectivity of a graph from 1 to 2"
    - "approximating unweighted tree augmentation via lift and project part ii"
    - "lp based algorithms for capacitated facility location"

Connected through hyperedge HE-5 (induced by source paper "coloring down 3 2 approximation for special cases of the weighted tree augmentation problem"):
  with members:
    - "a frac 3 2 approximation algorithm for tree augmentation via chvatal gomory cuts"
    - "improved approximation for weighted tree augmentation with bounded costs"
    - "approximating unweighted tree augmentation via lift and project part i stemless tap"
    - "a 1 75 lp approximation for the tree augmentation problem"
    - "approximating unweighted tree augmentation via lift and project part ii"

Question: Please tell me which class the center node belongs to. The 40 classes are: cs.NA(Numerical Analysis), cs.MM(Multimedia), cs.LO(Logic in Computer Science), cs.CY(Computers and Society), cs.CR(Cryptography and Security), cs.DC(Distributed, Parallel, and Cluster Computing), cs.HC(Human-Computer Interaction), cs.CE(Computational Engineering, Finance, and Science), cs.NI(Networking and Internet Architecture), cs.CC(Computational Complexity), cs.AI(Artificial Intelligence), cs.MA(Multiagent Systems), cs.GL(General Literature), cs.NE(Neural and Evolutionary Computing), cs.SC(Symbolic Computation), cs.AR(Hardware Architecture), cs.CV(Computer Vision and Pattern Recognition), cs.GR(Graphics), cs.ET(Emerging Technologies), cs.SY(Systems and Control), cs.CG(Computational Geometry), cs.OH(Other Computer Science), cs.PL(Programming Languages), cs.SE(Software Engineering), cs.LG(Machine Learning), cs.SD(Sound), cs.SI(Social and Information Networks), cs.RO(Robotics), cs.IT(Information Theory), cs.PF(Performance), cs.CL(Computation and Language), cs.IR(Information Retrieval), cs.MS(Mathematical Software), cs.FL(Formal Languages and Automata Theory), cs.DS(Data Structures and Algorithms), cs.OS(Operating Systems), cs.GT(Computer Science and Game Theory), cs.DB(Databases), cs.DL(Digital Libraries), cs.DM(Discrete Mathematics). Directly output the class name.

gpt: cs.DS(Data Structures and Algorithms)