Diophantine equations: Euclidean domains
Construction of projective planes: splitting fields and finite fields
Error codes: primitive elements and subfields
Construction of primitive polynomials: cyclotomic polynomials and factorization
Ruler and compass construction: irreducibility and constructibility
Pappus' theorem and Desargues' theorem in projective planes: Wedderburn's theorem
Solution of polynomials by radicals: Galois groups
Crytography: elliptic curves and factorization.