where the sum runs over all ( N r ) distinct sets of r indices, and, for each such set, { i 1 , … … , i r } , J i 1 , … … , i r is an independent Gaussian variable of mean 0 and variance J 2 r ! / ( 2 N r − − 1 ) , the Random-Energy model is recovered in the r → → ∞ ∞ limit.