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I am looking for an expository text on the paper "The classification of simply connected manifolds of positive scalar curvature" by Gromov and Lawson, in particular on the proof of Theorem A....

Recall that a surgery of codimension $q$ on an $n$-manifold $X$ is a modification of $X$ of the following type. Let $\Sigma^{n-q}\subset X$ be a smoothly embedded $(n-q)$-sphere with a trivialized ...