 Additional topics related to PDL include results concerning comparative power of expression, decidability, complexity, and completeness of a number of interesting variants obtained by extending or restricting PDL in various ways.  Since its inception, many variants of PDL have received attention. These variants may consider deterministic programs, restricted tests, non-regular programs, programs as automata, complementation and intersection of programs, converse and infinite computations, etc. We will present some of them in section 4, providing some pointers regarding their relative expressivity, their axiomatizations, and their computational complexity. 