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Models of any consistent set of clauses S **are arranged in clusters, each**
determined by a satisfying path P
(k) and so containing N = 2B−k **models that**
have k literals in common. In such a cluster the evidence of all k = B − log2 N common literals is 1, and that of each of the rest of log2 N literals is 0.**5. Hence**
the average evidence of an atom in a cluster is 1 − (log2 N)/(2B**). So for a**
system S with M models 1 − (log2 M)/(2B**) can be taken as an approximation** of E(S). If 1−(log2 M)/(2B) is substituted for E(S**) in expression (18) then the**
right-hand side of (18) has a minimum at a number of models M0 **determined**
by equation
$(1-\phi)\ln(1-\phi)+\frac{1}{2\ln2}\phi^{1-1/B}=0$  $M_{0})/(2B))^{B}$. Since the number of mod 
1−1/B **= 0 (22)**
where φ = (1 − (log2 M0)/(2B))B. Since the number of models of S is a monotone decreasing function of r, there is a value r0 corresponding to M0 **at which**
p(mtm) has a minimum as shown in Figure 2. It is worth noting that the erratum of a most typical model decreases with growing value of r**. This is in**
agreement with the common-sense intuition that the more information a system contains, the more right conclusions can be derived.

The clauses-to-variables ratio r of S **can be calculated in time linear in**

$\downarrow$ 2. 

$\uparrow$, cf. 