prd_boolSent :: BOOL_SENT -> Set.Set NAME
prd_boolSent b =
    case b of
         Conjunction ss -> unifyPredicates prd_sentence ss
         Disjunction ss -> unifyPredicates prd_sentence ss
         Negation s -> prd_sentence s
         Implication s1 s2 -> unifyPredicates prd_sentence [s1,s2]
         Biconditional s1 s2 -> unifyPredicates prd_sentence [s1,s2]
prd_boolSent :: BOOL_SENT -> Set.Set NAME
prd_boolSent b =
    case b of
         Conjunction ss -> unifyPredicates prd_sentence ss
         Disjunction ss -> unifyPredicates prd_sentence ss
         Negation s -> prd_sentence s
         Implication s1 s2 -> unifyPredicates prd_sentence [s1,s2]
         Biconditional s1 s2 -> unifyPredicates prd_sentence [s1,s2]
prd_boolSent b =
    case b of
         Conjunction ss -> unifyPredicates prd_sentence ss
         Disjunction ss -> unifyPredicates prd_sentence ss
         Negation s -> prd_sentence s
         Implication s1 s2 -> unifyPredicates prd_sentence [s1,s2]
         Biconditional s1 s2 -> unifyPredicates prd_sentence [s1,s2]