Primary scan: oa.ee.tsinghua.edu.cn/ouzhijian/pgm/pgm-pdf/Robbins%26Monro1951_a%20stochastic%20approximation%20method.pdf . Annals of Mathematical Statistics 22(3), 400–407. Title page verifies both full bylines. Sections 1–3 introduce noisy mean-response root finding and the diminishing-step recursion; convergence requires the paper’s response and step-size hypotheses.