private fun retrieve_vt_bound(anchor: MClassType, mtype: nullable MType): MType do
		if mtype == null then
			print "NOT YET IMPLEMENTED: retrieve_vt_bound on null"
			abort
		end
		if mtype isa MVirtualType then
			return mtype.anchor_to(mainmodule, anchor)
		else if mtype isa MParameterType then
			return mtype.anchor_to(mainmodule, anchor)
		else
			return mtype
		end
	end