// We have this enum.
enum Formula {
  case proposition(String)
  indirect case negation(Formula)
  indirect case operation(op: String, lhs: Formula, rhs: Formula)

  var nnf: Formula { /* ... */  }
}

// And now ...

switch formula.nnf {
 case .proposition(_):
   return formula.nnf
 case .negation(_):
   return formula.nnf
 case .operation(_, _, _):
   return formula.nnf
}

        var validAccountData = account.email != nil
        validAccountData = account.firstName != nil
        validAccountData = account.lastName != nil
        
        if validAccountData {
            return account
        }
        
        return nil

if let _ = detailInformation {
     loadDetailInformation()
}

guard let reachability = Reachability(), reachability.isReachable == true else {
    // No network connection available. Do stuff.
    ...
}