>>393 補足

モストフスキ崩壊補題の原論文PDFが下記にあるね
”1949,?theorem 3”らしい
https://en.wikipedia.org/wiki/Mostowski_collapse_lemma
Mostowski collapse lemma
(抜粋)
In mathematical logic, the Mostowski collapse lemma, also known as the Shepherdson?Mostowski collapse, is a theorem of set theory introduced by Andrzej Mostowski (1949,?theorem 3) and John Shepherdson (1953).

References
http://matwbn.icm.edu.pl/ksiazki/fm/fm36/fm36120.pdf
Mostowski, Andrzej (1949), "An undecidable arithmetical statement" (PDF), Fundamenta Mathematicae, Institute of Mathematics Polish Academy of Sciences, 36 (1): 143?164