private fun lookup_single_definition(mmodule: MModule, resolved_receiver: MType): MVirtualTypeDef
	do
		assert not resolved_receiver.need_anchor
		var props = self.mproperty.lookup_definitions(mmodule, resolved_receiver)
		if props.is_empty then
			abort
		else if props.length == 1 then
			return props.first
		end
		var types = new ArraySet[MType]
		var res  = props.first
		for p in props do
			types.add(p.bound.as(not null))
			if not res.is_fixed then res = p
		end
		if types.length == 1 then
			return res
		end
		abort
	end