@MISC{Moerdijk99wellfoundedtrees, author = {Ieke Moerdijk and Erik Palmgren}, title = {Wellfounded Trees in Categories}, year = {1999}}
dependent product freyd cover gluing category explicit calculation realizability topos internal sheaf explicit description categorical characterization categorical definition categorical construction martin-lof type theory standard definition wellfounded tree basic functoriality property weak predicative metatheory