Problem 18.6. Suppose Sigma$\Sigma$ is a recursive set of sentences of LN.
Find a sentence of LN, which we'll denote by Con(Sigma),$Con(\Sigma)$, such that Sigma$\Sigma$ is
consistent if and only if $A |-Con(Sigma)\vdashCon(\Sigma)$.
By Godel's second incompleteness theorem isn't this impossible?