I've been reading the book "Some applications of modular forms" by Peter Sarnak. On page 25, where he is trying to find a bound for the Fourier coefficients of the Poincaré series the notation $O_{\epsilon}(c^{1/2+ \epsilon})$ comes up. I am familiar with the "Big O" notation but I haven't had any luck about finding this one online.
Thank you in advance.