  Extremal Combinatorics is among the most active topics in Discrete
Mathematics, dealing with problems that are often motivated by questions in
other areas, including Theoretical Computer Science and Information Theory.
This paper contains a collection of problems and results in the area, including
solutions or partial solutions to open problems suggested by various
researchers. The topics considered here include questions in Extremal Graph
Theory, Coding Theory and Social Choice. This is by no means a comprehensive
survey of the area, and is merely a collection of problems, results and proofs,
which are hopefully interesting. As the title of the paper suggests, this is a
sequel of three previous papers of the same flavour. Each section of this paper
is essentially self contained, and can be read separately.
