Adding holes and crosscaps to the superstring

A hole or crosscap in the world sheet of a superstring creates the eigenstate of the quantized boundary conditions. This observation makes the calculation of open string loop divergences almost trivial. We confirm that the O(32) theory is finite. In other theories, the divergences induce BRST anomalies. Cancelling them against the tree-level BRST anomalies of the sigma model gives the loop-corrected equations of motion without ambiguities. (orig.)