Invitation to higher local fields, Part I, section A: Appendix to   Section 2
  This appendix discusses some basic definitions and properties of differential forms and Kato's cohomology groups in characteristic p and a sketch of the proof of Bloch-Kato-Gabber's theorem which describes the differential symbol from the Milnor K-group K_n(F)/p of a field F of positive characteristic p to the differential module \Omega_F^n. 
Masato Kurihara and Ivan Fesenko