DIFFERENTIAL SUBGROUPS OF SIMPLE ALGEBRAIC-GROUPS OVER P-ADIC FIELDS

A theorem of Cassidy states that any Zariski closed differential algeb raic subgroup of a simple linear algebraic group, defined over a diffe rential field, is either the whole group or is conjugate to the subgro up of constant matrices. An arithmetic analogue of this theorem is pro ved in which usual derivations on fields are replaced by certain nonli near operators on p-adic rings, called ''p-derivations.''