The definition of a class
C of functions is
syntactic if membership to
C can be decided from the construction of its elements. Syntactic characterizations of PTIMEF, of PSPACEF, of the polynomial hierarchy PH, and of its subclasses
n
p
are presented. They are obtained by progressive restrictions of recursion in Lisp, and may be regarded as
predicative according to a foundational point raised by Leivant.