The countable existentially closed pseudocomplemented semilattice
  As the class of pseudocomplemented semilattices is a universal Horn class generated by a single finite structure it has a $\aleph_0$-categorical model companion. We will construct the countable existentially closed pseudocomplemented semilattice which is the uniquely determined model of cardinality $\aleph_0$ of the model companion as a direct limit of algebraically closed pseudocomplemented semilattices. 
Jo\"el Adler
math.LO