\chapter*{Acknowledgements}

A thesis is never written by a single person alone. I've enjoyed a lot of
support from various people and I would like to take a moment to thank them:

My supervisors Johan Jeuring and Jos\'e Pedro Magalh\~aes have always and
patiently answered my many questions, offering hints whenever I was stuck and
gently guiding me in a good direction.

My sisters, parents and grandparents have continuously supported me through
their love and patience.

Most of the work for this thesis was done in the students lab at the Software
Technology group at university. Situated conveniently close to the offices of
professors, teachers and researchers, I was often able ask them for advice.
Notably Andres L\"oh and Stefan Holdermans have helped me significantly, for
example by answering complicated questions about higher-order typery.

Also present in the students lab were other students working on various
projects. There was often someone to exchange thoughts with and also to be
distracted by. Of these, Chris Eidhof, Erik Hesselink, Jeroen Leeuwestein,
Mathijs Swint, Sebastiaan Visser and Tom Lokhorst deserve special mention.

Sjoerd Visscher, my colleague at Q42/Xopus, has provided me with many a
helpful hint or thought. An exchange of emails with Conor McBride and my visit
to GTTSE in Braga, Portugal have also been insightful. Ralf L\"ammel has
provided me with some helpful pointers.

Thank you!