For any smooth projective variety X of dimension n over an algebraically closed field k of characteristic p > 0 with μ(Ω X ) > 0. If T(Ω X ) (0 < l < n(p − 1)) are semi-stable, then the sheaf B X of exact 1-forms is stable. When X is a surface with μ(Ω X ) > 0 and Ω X is semi-stable, the sheaf B X of exact 2-forms is also stable. Moreover, under the same condition, the sheaf Z X of closed 1-for...