Flavio Antonio Ferrarotti Jose Maria Turull Torres Arity and alternation: a proper hierarchy in higher order logics. 111-141 2007 50 Ann. Math. Artif. Intell. 1-2 http://dx.doi.org/10.1007/s10472-007-9071-4 db/journals/amai/amai50.html#FerrarottiT07