Appendix.

Notations

• $c(G)$,
  • number of components in the graph $G$
• $c(\Sigma)$
  • Euler charactisti of surface $\Sigma$,
• $c(a)$
  • capacity or cost of arc in network
• $c(x, y)$,
  • least size of cut separating two given vertices
• $c(\mathcal{F}, G)$,
  • number of overs by family of graphs