Sequence of elements

Hello. Is it possible to have an number of elements in an arbitrary
sequence an arbitrary number of times?I mean, for an xml like this

<lala>
	<foo/>
	<foo/>
	<bar/>
	<foo/>
	<boo/>
</lala>

I want any possible sequence of foo,bar and boo in the xml any possible
number of times. How do I write the xsd for this? Is it possible?

Thanks a lot!

Stam