B. Dwork: On the rationality of the zeta function of an algebraic variety.
Am. J. Math. 82 (1960), 631-648.

B. Dwork: On the zeta function of a hypersurface.
Publ. IHES 12 (1962), ...

B. Dwork: On the zeta function of a hypersurface II.
Annals Math. 80 (1964), 227-239.