3 problems

For a graph class $\mathcal{G}$, let $\operatorname{obs}(\mathcal{G})$ denote its minor obstruction set. For a class property $\mathbb{C}$, let $\operatorname{cobs}(\mathbb{C})$ be…

For a graph class $\mathcal{G}$, let $\operatorname{obs}(\mathcal{G})$ denote its minor obstruction set. For a class property $\mathbb{C}$, let $\operatorname{cobs}(\mathbb{C})$ be…

A graph is $n$-apex if deleting $n$ or fewer vertices results in a planar graph. A graph is a minor of another graph if it can be obtained by contracting edges in a subgraph. Let…