Daniel Leivant Feasible functionals and intersection of ramified types. 2002 70 Electr. Notes Theor. Comput. Sci. 1 http://www1.elsevier.com/gej-ng/31/29/23/125/51/show/Products/notes/index.htt#010 db/journals/entcs/entcs70.html#Leivant02