Relaxing the Irrevocability Requirement for Online Graph Algorithms

Online graph problems are considered in models where the irrevocability requirement is relaxed. We consider Late Accept model, a request can be accepted at later point, but any acceptance irrevocable. Similarly, we Reject an rejected, rejection irrevocable (this sometimes called preemption). Finally, Accept/Reject late accepts and rejects both allowed, reject four classical problems: For Maximum Independent Set, model necessary to obtain constant competitive ratio, for Minimum Vertex Cover sufficient, Spanning Forest sufficient. The Matching problem admits ratios all cases. also Acyclic Subgraph Planar Subgraph, which exhibit patterns similar Set.