Some conceptual issues involving probability in quantum mechanics
  We discuss some issues about probability in quantum mechanics, with particular emphasis on the GHZ theorem. We propose the usage of nonmonotonic upper probabilities as a tool to derive consistent joint upper probabilities for systems where only contextual hidden variables are possible. 
J. Acacio de Barros ((1) and (2)) and Patrick Suppes (1) ((1) Stanford   University, USA (2) UFJF, MG, Brazil)