[Avodah] gzeira shyava

[Rich, Joel]

The gemara in R"H 2b learns what seems to be a gzeirah shava of 20/20. Rashi comments that Rav Papa learned the specific application from his rebbi "al yidei gzeira shava." However, both the Ritva and Aruch L'nair state it's not a "real" gzeirah shavah because it's not mufneh (open, word not needed). 1.) Is this a disagreement in tradition? 2.) We see elsewhere a gzeirah shava which isn't mufneh (just that it can be logically rebutted). So, why not here?
KT
Joel Rich

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