• Subdirect Products (Burris and Sankappanavar, Ch.II.8, pages 57-59)
  • The lattice of congruences of a subdirectly irreducible algebra
  • Birkhoff's Theorem (every algebra is isomorphic to a subdirect product of subdirectly irreducible algebras).
• Free Algebras; Terms, Term algebras; Identities (Burris and Sankappanavar, Ch.II.10, pages 62-66)