In mathematics, more specifically differential algebra, a p-derivation (for p a prime number) on a ring R, is a mapping from R to R that satisfies certain conditions outlined directly below. The notion of a p-derivation is related to that of a derivation in differential algebra.
Let p be a prime number. A p-derivation or Buium derivative on a ring is a map that satisfies the following "product rule":
and "sum rule":
as well as
Note that in the "sum rule" we are not really dividing by p, since all the relevant binomial coefficients in the numerator are divisible by p, so this definition applies in the case when has p-torsion.
A map is a lift of the Frobenius endomorphism provided . An example of such a lift could come from the Artin map.
If is a ring with a p-derivation, then the map defines a ring endomorphism which is a lift of the Frobenius endomorphism. When the ring R is p-torsion free the correspondence is a bijection.
The quotient is well-defined because of Fermat's little theorem.
defines a p-derivation.
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