  In the first formalization of the Red Barn Example, logical  derivation will be performed in a basic modal logic in which \(\Box\)   is interpreted as the ‘belief’ modality. Then some of the occurrences of \(\Box\)  will be externally interpreted as  ‘knowledge’ according to the problem’s description. Let  \(B\) be the sentence ‘the object in front of me is a  barn’, and let \(R\) be the sentence ‘the object in  front of me is red’.