A 1-removed subgraph G_f G f of a graph G=(V,E) G = ( V , E ) is obtained by (i) selecting
at most one edge f ( v ) for each vertex v\in V v ∈ V , such that v\in f(v)\in E v
∈ f ( v ) ∈ E (the mapping f:V\rightarrow E \cup \{\varnothing \} f : V → E ∪ { ∅
} is allowed to be non-injective), and (ii) deleting all the selected edges f ( v
) from the edge set E of G .
