[NTG-context] amssymb

Dear Sirs, I have a problem with displaying some special characters from the AMS Symbol-fontset, e.g. \blacksquare, \blacktriangle, ... The symbols are displayed under MkII but not under MkIV. (MkII and MkIV-version: 2010.05.24) The symbols are defined in "math-ent.lua", but how can I call this file to show the missing symbols? Is it possible to make a link to the now-non-existing Module "amsl" so I can use old ConTeXt-documents without changes? Thanks for your help Bernd Kosubek