An elementary formula for entanglement entropies of fermionic systems
  An elementary formula for the von Neumann and Renyi entropies describing quantum correlations in two-fermionic systems having four single particle states is presented. An interesting geometric structure of fermionic entanglement is revealed. A connection with the generalized Pauli principle is established. 
P\'eter L\'evay, Szilvia Nagy and J\'anos Pipek