feat(ring_theory/witt_vector/frobenius): the frobenius endomorphism of witt vectors (#4838)
feat(ring_theory/witt_vector/frobenius): the frobenius endomorphism of witt vectors (#4838)

Co-Authored-By: Rob Y. Lewis <597e2d195b18d1f0b2b6530cee088a0ab0ed3ce2@gmail.com>



Co-authored-by: Rob Lewis <597e2d195b18d1f0b2b6530cee088a0ab0ed3ce2@gmail.com>

leanprover-community/mathlib,leanprover-community/mathlib