free_formula :: CASLFORMULA -> CASLFORMULA
free_formula (Quantification q vs f r) = Quantification q vs' f' r
     where vs' = free_var_decls vs
           f' = free_formula f
free_formula :: CASLFORMULA -> CASLFORMULA
free_formula (Quantification q vs f r) = Quantification q vs' f' r
     where vs' = free_var_decls vs
           f' = free_formula f
free_formula (Quantification q vs f r) = Quantification q vs' f' r
     where vs' = free_var_decls vs
           f' = free_formula f