public static HMap <A, HMap <B, HMap <C, HMap <D, T> > > > FilterRemoveT <A, B, C, D, T>(this HMap <A, HMap <B, HMap <C, HMap <D, T> > > > self, Func <T, bool> pred) { return(self.MapRemoveT(v => v.Filter(pred))); }