1. ## Graph problem(euler,hamilton,color)

I would like a little help on that pleace..

Let be n1,n2 such natural numbers that n1>=3 and n2>=3 and let be C(n1,n2) a graph that takes shape by taking Cn1, the circle of n1 vertices, and Cn2 the circle of n2 vertices, and linking all of Cn1 vertices with all of Cn2 vertices.
a) For which values of n1,n2 has the graph C(n1,n2) an Euler circle ?
b) For which values of n1,n2 has the graph C(n1,n2) a Hamilton circle ?
c) For which values of n1,n2 is the graph C(n1,n2) a 5 -colorable but no 4-colorable?
Indication: Show first that in each legal coloration C (n1, n2), the sets of colours that are used for Cn1 vertices and Cn2 vertices they have to to be foreign from each other.

2. Just look up the definitions of your problem. So as an example, to find a Hamiltonian cycle, you want to find a tour which visits each vertex once and which starts and ends in the same vertex. So somehow you need to pass through all the vertices in the outer cycle, as well as the vertices in the inner cycle, without passing through a vertex twice. So basically you can walk over all the vertices in the outer cycle, than move to the inner cycle, walk over the inner cycle and return to the outer cycle. At least, this should be possible because you state that all vertices of the outer graph are connected with all vertices in the inner graph?