Some useful substitutions -- Always Cauchy-Schwarz... --- Look at the exponent -- Primes and squares -- T2's lemma -- Some classical problems in extremal graphy theory -- Complex combinatorics -- Formal series revisited -- A brief introduction to algebraic number theory -- Arithmetic properties of polynomials -- Lagrange interpolation formula -- Higher algebra in combinatorics -- Geometry and numbers -- The smaller, the better -- Density and regular distribution -- The digit sum of a positive integer -- At the border of analysis and number theory -- Quadratic reciprocity -- Solving elementary inequalities using integrals --Pigeonhole principle revisited -- Some useful irreducibility criteria -- Cycles, paths, and other ways -- Some special applications of polynomials