mathlib

b707e989 - refactor(ring_theory/witt_vector): move lemmas to separate file (#4693)

refactor(ring_theory/witt_vector): move lemmas to separate file (#4693) This new file has almost no module docstring. This is on purpose, it is a refactor PR. A follow-up PR will add a module docstring and more definitions. Co-Authored-By: Rob Y. Lewis <rob.y.lewis@gmail.com>