- Make [Highord.pred 'a] an alias for [Highord.func 'a bool],
rename [Highorg.(@!)] to [(@)], remove [Highorg.(@?)], remove
the quantifiers [\!] and [\?] and only leave [\] which is the
only true lambda now;
- Allow mixing bool and Prop in logic, Dterm will introduce
coercions where necessary (trying to minimize the number of
if-then-else in the term context).