Improved bounds for the number of forests and acyclic orientations in the square lattice.
Bipartite graphs G = (L,R;E) and H = (L’,R’;E’) are bi-placeabe if there is a bijection f:L∪R→ L’∪R’ such that f(L) = L’ and f(u)f(v) ∉ E’ for every edge uv ∈ E. We prove that if G and H are two bipartite balanced graphs of order |G| = |H| = 2p ≥ 4 such that the sizes of G and H satisfy ||G|| ≤ 2p-3 and ||H|| ≤ 2p-2, and the maximum degree of H is at most 2, then G and H are bi-placeable, unless G and H is one of easily recognizable couples of graphs. This result implies easily that for integers...
A subset of the vertex set of a graph is called dominating in , if each vertex of either is in , or is adjacent to a vertex of . If moreover the subgraph of induced by is regular of degree 1, then is called an induced-paired dominating set in . A partition of , each of whose classes is an induced-paired dominating set in , is called an induced-paired domatic partition of . The maximum number of classes of an induced-paired domatic partition of is the induced-paired domatic...