2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/147146We correct some errors in the earlier version of this paper. Most importantly, the definition of isogeny of marked stable graphs has changed.Postscript file available at http://www.math.ubc.ca/people/faculty/behrend/gwi.ps , AMSLaTeXAlgebraic Geometrytext