Proof with chromatic index.
140444
Prove $\chi(G)\chi(\bar{G}) \geq n$ for chromatic number of graph and its complement
126060
Proving that a Euler Circuit has a even degree for every vertex
71990
Prove there always exists a partition such that vertices in each part have even degree
152696
Proof of LOOCV formula
146933
Proving bipartition in a connected planar graph
46309
Prove that this graph is nonplanar
24477
Monochromatic squares in a colored plane
28658
$R$ with an upper bound for degrees of irreducibles in $R[x]$
37984
Prove a planar graph with all regions having even degree can be colored with 2 colors
40858
Multiplicative nature of the separability degree
48397
Index of a sublattice in a lattice and a homomorphism between them
154564
Prove that the sum of minimum edge cover and maximum matching is the vertex count
78685
How to find all proper colorings (four coloring) of a graph with a brute force algorithm
38700
the Nordhaus-Gaddum problems for chromatic number of graph and its complement
35458
Prove, that graph $G$ has at least $\chi(G)(\chi(G)-1)/2$ edges.
45958
Proof that the Euler characteristic is additive
36660
Question about the proof of Ramsey's Theorem