Graphs-1

4. Proved with Appel the Four Color Conjecture
8. Vertex in a graph whose removal increases the number of components
10. Oriented complete graph
12. Conjectured that any connected n-chromatic graph is contractible to K_n
13. Graph for which it is possible to find a walk that traverses each vertex exactly once, goes through each vertex and ends at the starting point
14. Graph possessing no odd cycles
15. Conjectured that any square of 2-connected graphs is Hamiltonian
16. Showed in 1938 that abstract groups appear as groups associated to a graph
18. Developed the theory of trees in 1847
20. If every walk on a digraph is a path, then it is

1. Graph such that all its cycles are even
2. Shortest path joining two vertices
3. Showed that there is only one way to embed a 3-connected planar graph in the plane
5. Found in 1891 the error in Kempe's proof
6. Said of a digraph having a spanning closed walk
7. Pioneer in planarity problems of graphs
9. connected graph with no cycles
11. Said of two vertices that are endpoints of the same edge
17. Conned¡cited graph isomorphic to ops line graph
19. Combinatorial analogue of a continuous image of a closed line segment