A proof method for the six-valued logic for incomplete information

O. Garcia and M. Moussavi (1990) proposed a six-valued logic to model incomplete information. Although their logic is promising, it lacks a proof theory to serve as a basis for automated reasoning. We describe a sequent style proof method for the logic and show that the consequence relation in the logic is equivalent to the one by N.D. Belnap's (1977) four-valued logic. We also suggest alternative formal interpretations for the logic.