# Collect all virtual types introduced in `self`
	fun collect_intro_vts(filter: nullable ModelFilter): Set[MVirtualTypeProp] do
		var res = new HashSet[MVirtualTypeProp]
		for mproperty in collect_intro_mproperties(filter) do
			if mproperty isa MVirtualTypeProp then res.add(mproperty)
		end
		return res
	end