# OP\_NOTIF - Executing Code When False

<figure><img src="/files/bdSdSOIeTisIaY8aw6cE" alt=""><figcaption></figcaption></figure>

**OP\_NOTIF** is the logical inverse of OP\_IF. It executes the enclosed code block when the top stack item represents a **false value** (zero or empty).

#### Basic OP\_NOTIF structure:

```
<Expression>
OP_NOTIF
  <False action>
OP_ENDIF
```

#### How OP\_NOTIF evaluates stack values:

* **Zero or empty array** → Code block executes
* **Non-zero values** → Code block is skipped
* The top stack item is **consumed** by OP\_NOTIF

#### Comparison of OP\_IF vs OP\_NOTIF behavior:

| **Stack Top Value** | **OP\_IF Behavior** | **OP\_NOTIF Behavior** |
| ------------------- | ------------------- | ---------------------- |
| **Non-zero (TRUE)** | Execute block       | Skip block             |
| **Zero (FALSE)**    | Skip block          | Execute block          |
| **Empty array**     | Skip block          | Execute block          |

#### When to use OP\_NOTIF:

Use OP\_NOTIF when you want to execute code specifically on **failure conditions** or to implement **inverse logic** without adding negation operations. It's particularly useful for fallback spending conditions.

#### Practical example:

```
<primary_signature> <primary_pubkey> OP_CHECKSIG
OP_NOTIF
  <backup_signature> <backup_pubkey> OP_CHECKSIGVERIFY
OP_ENDIF
```

This script first attempts to validate with the primary signature. If primary signature fails (returns FALSE), **OP\_NOTIF**executes the backup verification, providing a **fallback spending path** when primary credentials aren't available.

**Grammar requirement:** Like OP\_IF, every OP\_NOTIF must have a matching **OP\_ENDIF**.


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