Pigeonhole Principle, Discrete Mathematics, Combinatorics, Mathematical Logic, Problem Solving.
that goes to 10 floors. How many people will go to the same floor? The 10 floors can be considered pigeonholes. As 12/10=2, at least 2 of them get off on the same floor. Application in graph theory Consider the following statement: Prove that in any simple graph containing a minimum of 2 vertices,