Prove that if a,x,y are p-adic integers different from 0 and p∣x,pa∣xy, then \frac 1y \frac{(1\plus{}x)^y\minus{}1}{x} \equiv \frac{\log (1\plus{}x)}{x} \;\;\;\; ( \textrm{mod} \; a\ ) \\\\ .
L. Redei logarithmssuperior algebrasuperior algebra unsolved