An old letter from J. Tate to B. Dwork, as viewed recently by J. Tate and B. Mazur

In this paper, the constant $C$, which is defined in the letter for a fixed ordinary elliptic curve, is viewed as a special value of formal function on a vast ind-profinite “Galois cover of the ‘Hasse Domain’ ” $H$ parametrizing all ordinary elliptic curves, viewed as a formal scheme.