Is parchment processed by a non-Jew (with a Jew's instruction and/or supervision) valid for tefillin?

Synopsis

The Rambam invalidates parchment processed by a non-Jew even if a Jew instructed him to do so lishmah. The Rosh holds it is valid if a Jew supervises and assists partially. The Rema rules in accordance with the Rosh, and this is the accepted custom.

Rishonim
Early Acharonim
Lenient
Strict
Lesser cited
Major authority

Discussion

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