Proof that N lines on a plane can be painted in 2 colors ,so that no 2 neighbor sectors , formed by this lines, are in the same color.
141482
Proof that plane with $N$ lines can be painted with two colors so that any two neighboring regions are painted in different colors
27478
Proof that two basis of a vector space have the same cardinality in the infinite-dimensional case
141101
Russia (2000) contest:Prove the existence of a pair of rows and columns with intersections differently coloured
116378
Nonhomeomorphic subsets of the plane
42270
Combinatorics - Painting the Unit Squares of a 3x3 Square
126583
Coloring points on an n-gon
100164
Tennis tournament proof that $n + 1$ players can form a line
16016
Coloring dodecahedron
152518
Proof that the set of all possible curves is of cardinality $\aleph_2$?
150707
Prove the statement 'World is not flat'
55486
Topological proof to show a complement set of a set is polygonally connected
156850
Fix-Point Theorem Proof.
155295
A solution to the Four-Color Theorem applied to the map Florida, USA
125668
A proof that BS(1,2) is not polycyclic
17086
The number of (non-equal) forests on the vertex set V = {1, 2, ...,n} that contains exactly 2 connected components is given by
7626
Proving that every connected graph has a vertex whose removal will not disconnect the graph.
101493
Prove that one diagonal of a quadrilateral bisects the other