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.