Spin observables in antiproton-proton to AntiLambda-Lambda and   density-matrix constraints
  The positivity conditions of the spin density matrix constrain the spin observables of the reaction antiproton-proton to AntiLambda-Lambda, leading to model-independent, non-trivial inequalities. The formalism is briefly presented and examples of inequalities are provided. 
Mokhtar Elchikh (Oran) Jean-Marc Richard (Grenoble)