What's the correct reference please for the proof that pasting/gluing two perfect graphs on a clique results in another perfect graph?

I think the correct ref is @article {Gal62, AUTHOR = {Gallai, T.}, TITLE = {Graphen mit triangulierbaren ungeraden {V}ielecken}, JOURNAL = {Magyar Tud. Akad. Mat. Kutat\'o Int. K\"ozl.}, VOLUME = {7}, YEAR = {1962}, PAGES = {336}, MRCLASS = {55.10}, MRNUMBER = {0145508 (26 #3039)}, MRREVIEWER = {J. W. Moon}, } 

