  A hole in a graph is an induced cycle of length at least 4. A hole is long if
its length is at least 5. By $P_t$ we denote a path on $t$ vertices. In this
paper we give polynomial-time algorithms for the following problems: the
Maximum Weight Independent Set problem in long-hole-free graphs, and the
Feedback Vertex Set problem in $P_5$-free graphs. Each of the above results
resolves a corresponding long-standing open problem.
  An extended $C_5$ is a five-vertex hole with an additional vertex adjacent to
one or two consecutive vertices of the hole. Let $\mathcal{C}$ be the class of
graphs excluding an extended $C_5$ and holes of length at least $6$ as induced
subgraphs; $\mathcal{C}$ contains all long-hole-free graphs and all $P_5$-free
graphs. We show that, given an $n$-vertex graph $G \in \mathcal{C}$ with vertex
weights and an integer $k$, one can in time $n^{\Oh(k)}$ find a maximum-weight
induced subgraph of $G$ of treewidth less than $k$. This implies both
aforementioned results.
