What has the author HPH Teesing written?

It appears you are referring to H.P.H. Teesing (sometimes listed as HPH Teesing). This Dutch author is most known for writing the "Dirk Gently's Holistic Detective Agency" series, a series of science fiction books that have been adapted into television series.

Here are some of his most notable works:

* Dirk Gently's Holistic Detective Agency (1987)

* The Long, Dark Tea-Time of the Soul (1995)

* The Salmon of Doubt (published posthumously in 2005)

Teesing, known for his quirky and humorous style, passed away in 2001, leaving the Dirk Gently series unfinished. He has been credited as a major influence in the science fiction genre.