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



Reference request: gluing/pasting perfect graphs on a clique?
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 = {3--36},
 MRCLASS = {55.10},
 MRNUMBER = {0145508 (26 #3039)},
MRREVIEWER = {J. W. Moon},
}


