1 if account A is opted in to application B, else 0
Txn.Accounts offset (or, since v4, an available account address), available application id (or, since v4, a Txn.ForeignApps offset).
1 if opted in and 0 otherwise.
Native TEAL opcode: app_opted_in Min AVM version: 2
app_opted_in
1 if account A is opted in to application B, else 0