According to Fermi-Dirac the statistics following assumption is made :
1
the particles are distinguishable and any number of particles may occupy the same energy level
2
the particles are indistinguishable and any number of particles may occupy a given energy level
3
the particles are indistinguishable but only one particle may occupy a given energy level
4
the particles are distinguishable and only one particle may occupy a given energy level
5
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