Leibniz, Jakob Bernoulli, and Euler accepted

$\frac{1}{1-(-1)}= 1 - 1 + 1 - 1 +-... = 1/2$

Wallis and Euler accepted

$\frac{1}{1-2}= 1 + 2 + 4  + ... = -1 > 1/0 > 1 $