         Sentence 1: If the apparant force of two  fermions is repulsive, what is the spin  function?         Sentence 2: However, already in quantum  mechanics there is one “caveat”, namely  the particles acting onto each other do  not only possess the spatial variable, but  also a discrete intrinsic angular  momentumike variable called the  "spin", and there is the Pauli principle  relating the space and the spin  variables.