Create Solana NFTs With Metaplex Core

Summary

Non-Fungible Tokens (NFTs) are onchain digital assets. They are indivisible, meaning they cannot be split into fractional parts, and unique.
Metadata attaches additional properties to Assets and Collection. Metadata includes the token name and a link to an offchain JSON file. This JSON file contains links to artwork and other media files, any special traits the NFT has, and more.
The Metaplex Core Program is an onchain program that sheds the complexity and technical debt of previous standards and provides a clean and simple core spec for digital assets using a single account design

Lesson

In this lesson, we'll explore how Core Assets are represented and demonstrate how to create and update them using the mpl-core SDK.

Solana Non-Fungible Tokens (NFTs) were commonly represented as SPL tokens with an additional metadata account associated with each token mint and created using both the Token Program and the Metaplex Token Metadata Program.

However, with the introduction of the new Metaplex Core Program, NFTs have their own program and standard that leverage a single account design and has a flexible plugin system that that enables developers to natively modify asset behavior and functionality

In this lesson, we'll explore how Core Assets are represented and demonstrate how to create and update them using the mpl-core SDK.

NFTs on Solana

All NFTs characteristics were previously achievable with a combination of the SPL Token Program and the Metaplex Token Metadata Program by setting the following boundaries:

0 decimals, so it cannot be divided into parts.
Supply of 1, so only 1 of these tokens exists.
No mint authority to ensure that the supply never changes.
Additional accounts including, Metadata, Master Edition and Token Record to store addotional information like name, uri, ... and inform that the previous boundaries are enforced.

This came with a big overhead and lots of inefficiencies for a market as big as NFTs and Digital Asset in general.

Thanks to the Metaplex Core Program, all this characteristics are now included at the protocol level!

The Metaplex Core program

The Metaplex Core Program is the newest NFT Digital Asset standard from Metaplex

Unlike the Token Metadata Program, Collections are separate accounts with a distinct data model from the Assets accounts. They store only collection-specific metadata, such as the collection name and collection image.
Assets are now a single account model and design that don't rely on additional accounts such as Associated Token Accounts or Metadata Accounts. Instead, when a Core Assets is created, the Metaplex Core Program stores the ownership and metadata directly on the Asset.
Both Assets and Collections can integrate with lifecycle events such as creation, transfer, and burning, enabling custom behaviors through Plugins. For instance, plugins allow features like royalty enforcement or on-chain attributes to be added with a single instruction, eliminating the need for extra code.

In the following sections, we'll cover the basics of using the metaplex-foundation/mpl-core SDK with Umi to prepare off-chain metadata, create and update Assets, and add them into a collection. For more information about metaplex-foundation/mpl-core visit the Metaplex Developer Docs.

Umi

Umi is a framework built by Metaplex that can register JS/TS clients built with Kinobi/Codama that interact with on-chain programs. While it can interface with clients from various programs, it's most commonly used with all the Metaplex programs.

Note: Umi uses different implementation types for common web3.js functions and concepts, such as Keypairs, PublicKeys, and Connections. Fortunately, it's easy to convert between web3.js and Umi equivalents.

For more deetails, visit the Metaplex Developer Docs.

Installing and setting up Umi

First, create a new Umi instance. We can do this by either providing our own RPC endpoint, or use the public facing Solana endpoints provided by the clusterApiUrl method.

import { createUmi } from "@metaplex-foundation/umi-bundle-defaults";
import { clusterApiUrl } from "@solana/web3.js";

const umi = createUmi(clusterApiUrl("devnet"));

Next, set the identity for your Umi instance (the keypair what will be used to sign transactions) and load the necessary plugins, in this case, the mplCore plugin.

import { mplCore } from "@metaplex-foundation/mpl-core";
import { keypairIdentity } from "@metaplex-foundation/umi";
import { createUmi } from "@metaplex-foundation/umi-bundle-defaults";
import { getKeypairFromFile } from "@solana-developers/helpers";
import { promises as fs } from "fs";

const umi = createUmi("https://api.devnet.solana.com").use(mplCore());

// load keypair from local file system
// See https://github.com/solana-developers/helpers?tab=readme-ov-file#get-a-keypair-from-a-keypair-file
const localKeypair = await getKeypairFromFile();

// convert to Umi compatible keypair
const umiKeypair = umi.eddsa.createKeypairFromSecretKey(localKeypair.secretKey);

// load the MPL metadata program plugin and assign a signer to our umi instance
umi.use(keypairIdentity(umiKeypair));

Uploading images

Before creating an Asset, you must prepare and upload any assets you plan to associate with it such as images, animation files, and off chain metadata.

Preparing and uploading an image involves converting to a buffer first. You can convert the file to a generic file using the createGenericFile() function and finally uploading it to the designated Storage Driver.

The GenericFile type allows Umi to support different file variations despite the difference of browser files and local file system files i.e. those on your computer.

In action, uploading an image named random-image.png from your computer would take the following steps:

Reading the file using fs.readFile() into a buffer.
Creating a generic file type with the files MIME Type from the buffer and filePath.
Uploading file to designated storage provider.

// Add an uploader to your umi instance. In this case we're going to use Irys
import { irysUploader } from "@metaplex-foundation/umi-uploader-irys";

// ...create Umi as shown before
umi.use(irysUploader());

let filePath = "random-image.png";

const buffer = await fs.readFile(filePath);
let file = createGenericFile(buffer, filePath, {
  // chose the correct file MIME type https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types
  contentType: "image/jpeg",
});
const [image] = await umi.uploader.upload([file]);

The function will return the uri where the image is stored.

Uploading the metadata

After uploading the image, it's time to upload the offchain JSON metadata using the uploadJson() method. This will return a uri where the JSON metadata is stored.

Remember, the offchain portion of the metadata includes things like the image uri we just generated as well as additional information like the name and description of the Asset. While you can technically include anything you'd like in this JSON object, in most cases, you should follow the standard JSON schema for Core to ensure compatibility with wallets, programs, and applications.

To create the metadata, use the uploadJson() method provided by the SDK. This method accepts a metadata object and returns a uri that points to the uploaded metadata.

const metadata = {
  name: "My NFT",
  description: "This is an NFT on Solana",
  image, // Uri of the Image
  external_url: "https://example.com",
  properties: {
    files: [
      {
        uri: image,
        type: "image/jpeg",
      },
    ],
    category: "image",
  },
};

const uri = await umi.uploader.uploadJson(metadata);

Now that you know how to create the metadata for your Collections and Assets, remember to modify the values as you see fit and use the response to fill out the uri field.

Creating the Collection

Once you have uploaded the appropiate files to respresent your Core Collection (image, metadata.json) you can finally create the Core Collection itself.

The createCollection method allows you to create a collection with the provided data

const collection = generateSigner(umi);
console.log("\nCollection Address: ", collection.publicKey.toString());

const { signature, result } = await createCollection(umi, {
  collection,
  name: "My Collection",
  uri: collectionUri,
}).sendAndConfirm(umi, { send: { commitment: "finalized" } });

The sendAndConfirm method is what takes care of signing our transaction and sending it. It also provides available options such as setting pre-flight checks and our desired commitment level for the transaction, which defaults to confirmed if not provided.

This method returns an object containing the transaction signature and a result. The result object contains the outcome of our transaction. If successful, the err inside this will be set to null otherwise it'll contain the error for the failed transaction.

By default, the SDK sets the payer and the updateAuthority property respecitvely using the payer and signer identity of the Umi instance we created previously like this:

const { signature, result } = await createCollection(umi, {
  ...createCollectionArgs,
  payer: umi.payer.publickey,
  updateAuthority: umi.identity.publicKey,
}).sendAndConfirm(umi, { send: { commitment: "finalized" } });

Creating the Asset

The create method allows you to create a new Asset similarly to how is done for Collections

const asset = generateSigner(umi);
console.log("\nAsset Address: ", asset.publicKey.toString());

const { signature, result } = await create(umi, {
  asset,
  name: "My Asset",
  uri: assetUri,
}).sendAndConfirm(umi, { send: { commitment: "finalized" } });

For this method there are two additional optional fields:

the owner field that if not supplied will default to the signer identity of the Umi instance like this:

const { signature, result } = await create(umi, {
  ...createArgs,
  owner: umi.identity.publicKey,
}).sendAndConfirm(umi, { send: { commitment: "finalized" } });

the collection field is only needed when we want to add the asset to a collection

const asset = generateSigner(umi);
const collection = await fetchCollection(
  umi,
  publicKey("CORE_COLLECTION_ADDRESS"),
);

const { signature, result } = await create(umi, {
  asset,
  collection,
  name: "My Asset",
  uri: assetUri,
}).sendAndConfirm(umi, { send: { commitment: "finalized" } });

Note: once you add an Asset to a Collection you'll need to pass in a CollectionV1 object in the collection field (can be obtained by using the fetchCollection() function) of subsequent instructions. Leaving the collection field empty will cause invalidations during transactions causing them to fail.

Updating the Asset & Collection

The following steps works for both Assets and Collection, the only difference will be employing the update method for Assets and the updateCollection method for Collections

The update method allows you to update all the fields present in the account like collection, name, updateAuthority and the uri

const asset = await fetchAsset(umi, publickey("CORE_ASSET_ADDRESS"));
const collection = await fetchCollection(umi, publicKey("CORE_ASSET_ADDRESS"));

const { signature, result } = await update(umi, {
  asset,
  collection,
  name: 'My new NFT'
  uri: newAssetUri
  newCollection: publicKey("NEW_CORE_COLLECTION_ADDRESS")
}).sendAndConfirm(umi, { send: { commitment: "finalized" } });

When we add an Asset to a Collection, to not waste any additional bytes, the collection gets stored in the updateAuthority field of the asset. So if you want to change the collection address for the asset, you can update the updateAuthority field of the update function, instead of using the newCollection field, like this:

const asset = await fetchAsset(umi, publickey("CORE_ASSET_ADDRESS"));
const collection = await fetchCollection(umi, publicKey("CORE_ASSET_ADDRESS"));

const { signature, result } = await update(umi, {
  asset,
  collection,
  newUpdateAuthority: updateAuthority("Collection", [
    publicKey("NEW_CORE_COLLECTION_ADDRESS"),
  ]),
}).sendAndConfirm(umi, { send: { commitment: "finalized" } });

Note: We can use the same method to add the Asset to a Collection if it isn't part of a collection currently.

A noted difference from the token-metadata program is that it not impossible to create an immutable Asset using the create method. The only way to make an asset immutable is to change the updateAuthority to None in a futher update.

const asset = await fetchAsset(umi, publickey("CORE_ASSET_ADDRESS"));
const collection = await fetchCollection(umi, publicKey("CORE_ASSET_ADDRESS"));

const { signature, result } = await update(umi, {
  asset,
  collection,
  newUpdateAuthority: updateAuthority("None"),
}).sendAndConfirm(umi, { send: { commitment: "finalized" } });

Note: any fields you don't include in the call to updateV1 will stay the same, by design.

Lab

In this lab, we'll go through the steps to create a Core Asset using the Metaplex Umi framework, add the Asset to the Collection and update its metadata in subsequent transactions. By the end, you will have a basic understanding of how to use the Metaplex Umi and the mpl-core SDK to interact with digital assets on Solana.

Part 1: Creating an Core collection

To begin, make a new folder and install the relevant dependencies:

npm i @solana/web3.js npm i @solana/web3.js npm i @solana-developers/helpers npm i @metaplex-foundation/mpl-core npm i @metaplex-foundation/umi-bundle-defaults npm i @metaplex-foundation/umi-uploader-irys npm i --save-dev esrun

Then create a file called create-metaplex-core-collection.ts, and add our imports:

import { createCollection, mplCore } from "@metaplex-foundation/mpl-core";
import {
  createGenericFile,
  generateSigner,
  keypairIdentity,
  percentAmount,
  sol,
} from "@metaplex-foundation/umi";
import { createUmi } from "@metaplex-foundation/umi-bundle-defaults";
import { irysUploader } from "@metaplex-foundation/umi-uploader-irys";
import {
  airdropIfRequired,
  getExplorerLink,
  getKeypairFromFile,
} from "@solana-developers/helpers";
import { clusterApiUrl, Connection, LAMPORTS_PER_SOL } from "@solana/web3.js";
import { promises as fs } from "fs";
import * as path from "path";

Connect to devnet, load a user and Airdrop some SOL if needed:

// create a new connection to Solana's devnet cluster
const connection = new Connection(clusterApiUrl("devnet"));

// load keypair from local file system
// See https://github.com/solana-developers/helpers?tab=readme-ov-file#get-a-keypair-from-a-keypair-file
// assumes that the keypair is already generated using `solana-keygen new`
const user = await getKeypairFromFile();

await airdropIfRequired(
  connection,
  user.publicKey,
  1 * LAMPORTS_PER_SOL,
  0.1 * LAMPORTS_PER_SOL,
);

console.log("Loaded user:", user.publicKey.toBase58());

Create a new Umi instance, assign it the loaded keypair, load the mplCore to interact with the metadata program and irysUploader to upload our files.

// create a new connection to Solana's devnet cluster
const umi = createUmi(connection).use(mplCore()).use(irysUploader());

// convert to umi compatible keypair
const umiKeypair = umi.eddsa.createKeypairFromSecretKey(user.secretKey);

// assigns a signer to our umi instance, and loads the MPL metadata program and Irys uploader plugins.
umi.use(keypairIdentity(umiKeypair));

Download the assets and collection image from the links below and save them inside your working directory:

We will use these images as our collection and asset cover images respectively.

We will use Irys as our storage provider that Metaplex conveniently supports through the umi-uploader-irys plugin, we can use that to upload our files. The plugin, also takes care of sending the right amount of lamports for storage fees so we don't have to worry about making this on our own.

Upload the offchain metadata to Irys:

const collectionImagePath = "collection.png";

const buffer = await fs.readFile(collectionImagePath);
let file = createGenericFile(buffer, collectionImagePath, {
  contentType: "image/png",
});
const [image] = await umi.uploader.upload([file]);
console.log("image uri:", image);

const metadata = {
  name: "My Collection",
  description: "My Collection description",
  image,
  external_url: "https://example.com",
  properties: {
    files: [
      {
        uri: image,
        type: "image/jpeg",
      },
    ],
    category: "image",
  },
};

// upload offchain json to Arweave using irys
const uri = await umi.uploader.uploadJson(metadata);
console.log("Collection offchain metadata URI:", uri);

Then actually create the collection:

// generate mint keypair
const collection = generateSigner(umi);

// create and mint a Collection
await createCollection(umi, {
  collection,
  name: "My Collection",
  uri,
}).sendAndConfirm(umi, { send: { commitment: "finalized" } });

let explorerLink = getExplorerLink("address", collection.publicKey, "devnet");
console.log(`Collection: ${explorerLink}`);
console.log(`Collection address is:  ${collection.publicKey}`);
console.log("✅ Finished successfully!");

We advise using esrun to run the scripts because it allows you to use top level await without having to wrap your code inside asynchronous function.

Run the create-metaplex-core-collection.ts script

npx esrun create-metaplex-core-collection.ts

The output should look like this:

% npx esrun create-metaplex-core-collection.ts
Loaded user: 2YkGRHjwD3jqcu4ie6pL9Axpdx5AKa6KDyj8bF473Vk5
image uri: https://arweave.net/EBRzcUrhbiTfSnx2oD1SZacGMbq2WeFtLUWSD5tAuP7
Collection offchain metadata URI: https://gateway.irys.xyz/HTK7UZsUqiVcnZ9ez2eNKPQLiU3Xg1hyic1ghwj6gXXE
Collection: https://explorer.solana.com/address/ACJgjrstigNsgukPuZWZay1L2DXeJPwTn6EyxB5hwWrK?cluster=devnet
Collection address is:  ACJgjrstigNsgukPuZWZay1L2DXeJPwTn6EyxB5hwWrK
✅ Finished successfully!

Congratulations! You've created a Metaplex Core Collection. Check this out on Solana Explorer using the URL above!

Keep the Collection addres since we're going to use it in the next step.

2. Creating a Core Asset and adding it to the Collection

We'll now create a Core Asset that's a member of the Collection we just Created.

Start by creating a new file called create-metaplex-core-asset.ts. The setup for this will look the same as the previous file, with slightly different imports:

import {
  mplCore,
  create,
  fetchCollection,
} from "@metaplex-foundation/mpl-core";
import {
  createGenericFile,
  generateSigner,
  keypairIdentity,
  publicKey as UMIPublicKey,
} from "@metaplex-foundation/umi";
import { createUmi } from "@metaplex-foundation/umi-bundle-defaults";
import { irysUploader } from "@metaplex-foundation/umi-uploader-irys";
import {
  airdropIfRequired,
  getExplorerLink,
  getKeypairFromFile,
} from "@solana-developers/helpers";
import { clusterApiUrl, Connection, LAMPORTS_PER_SOL } from "@solana/web3.js";
import { promises as fs } from "fs";
import * as path from "path";

// create a new connection to Solana's devnet cluster
const connection = new Connection(clusterApiUrl("devnet"));

// load keypair from local file system
// assumes that the keypair is already generated using `solana-keygen new`
const user = await getKeypairFromFile();
console.log("Loaded user:", user.publicKey.toBase58());

await airdropIfRequired(
  connection,
  user.publicKey,
  1 * LAMPORTS_PER_SOL,
  0.1 * LAMPORTS_PER_SOL,
);

const umi = createUmi(connection).use(mplCore()).use(irysUploader());

// convert to umi compatible keypair
const umiKeypair = umi.eddsa.createKeypairFromSecretKey(user.secretKey);

// assigns a signer to our umi instance, and loads the MPL metadata program and Irys uploader plugins.
umi.use(keypairIdentity(umiKeypair));

We can then put out files into Irys:

const assetImagePath = "asset.png";

const buffer = await fs.readFile(assetImagePath);
let file = createGenericFile(buffer, assetImagePath, {
  contentType: "image/png",
});

// upload image and get image uri
const [image] = await umi.uploader.upload([file]);
console.log("image uri:", image);

const metadata = {
  name: "My Asset",
  description: "My Asset Description",
  image,
  external_url: "https://example.com",
  attributes: [
    {
      trait_type: "trait1",
      value: "value1",
    },
    {
      trait_type: "trait2",
      value: "value2",
    },
  ],
  properties: {
    files: [
      {
        uri: image,
        type: "image/jpeg",
      },
    ],
    category: "image",
  },
};

// upload offchain json using irys and get metadata uri
const uri = await umi.uploader.uploadJson(metadata);
console.log("Asset offchain metadata URI:", uri);

Then we create an Asset and we add it to the Collection we just created:

// Substitute in your collection NFT address from create-metaplex-nft-collection.ts
const collection = await fetchCollection(
  umi,
  UMIPublicKey("YOUR_COLLECTION_ADDRESS_HERE"),
);
const asset = generateSigner(umi);

// create and mint NFT
await create(umi, {
  asset,
  collection,
  name: "My Asset",
  uri,
}).sendAndConfirm(umi, { send: { commitment: "finalized" } });

let explorerLink = getExplorerLink("address", asset.publicKey, "devnet");
console.log(`Asset: ${explorerLink}`);
console.log(`Asset address: ${asset.publicKey}`);

Run npx esrun create-metaplex-core-asset. If all goes well, you will see the following:

% npx esrun create-metaplex-core-asset
Loaded user: 2YkGRHjwD3jqcu4ie6pL9Axpdx5AKa6KDyj8bF473Vk5
image uri: https://arweave.net/79wKgR6VAuS3RfneBCNx3RMxzhAPUdqBaK4Ah4KQuWAr
Asset offchain metadata URI: https://gateway.irys.xyz/7F7YdG9mGFXaq51qPbog5QmymovansiipABtM2nDNLAV
Asset: https://explorer.solana.com/address/BXfRBtgVRmEnwQaLqCAproeuSMNdkgWYptHvjvHekHht?cluster=devnet
Asset address: BXfRBtgVRmEnwQaLqCAproeuSMNdkgWYptHvjvHekHht
✅ Finished successfully!

Inspect your Asset at the address given to confirm that the asset has been minted!

3. Update the NFT

Create a new file, called update-metaplex-core-asset.ts. The imports will be similar to our previous files:

import {
  mplCore,
  update,
  fetchAsset,
  fetchCollection,
} from "@metaplex-foundation/mpl-core";
import {
  createGenericFile,
  generateSigner,
  keypairIdentity,
  percentAmount,
  publicKey as UMIPublicKey,
} from "@metaplex-foundation/umi";
import { createUmi } from "@metaplex-foundation/umi-bundle-defaults";
import { irysUploader } from "@metaplex-foundation/umi-uploader-irys";
import {
  airdropIfRequired,
  getExplorerLink,
  getKeypairFromFile,
} from "@solana-developers/helpers";
import { clusterApiUrl, Connection, LAMPORTS_PER_SOL } from "@solana/web3.js";
import { promises as fs } from "fs";
import * as path from "path";

// create a new connection to Solana's devnet cluster
const connection = new Connection(clusterApiUrl("devnet"));

// load keypair from local file system
// See https://github.com/solana-developers/helpers?tab=readme-ov-file#get-a-keypair-from-a-keypair-file
// assumes that the keypair is already generated using `solana-keygen new`
const user = await getKeypairFromFile();
console.log("Loaded user:", user.publicKey.toBase58());

await airdropIfRequired(
  connection,
  user.publicKey,
  1 * LAMPORTS_PER_SOL,
  0.1 * LAMPORTS_PER_SOL,
);

// create a new connection to Solana's devnet cluster
const umi = createUmi(connection).use(mplCore()).use(irysUploader());

// convert to umi compatible keypair
const umiKeypair = umi.eddsa.createKeypairFromSecretKey(user.secretKey);

// assigns a signer to our umi instance, and loads the MPL metadata program and Irys uploader plugins.
umi.use(keypairIdentity(umiKeypair));

Fetch both Asset and Collection, using the address from the previous example and try to update the uri and the name of the Asset:

const assetImagePath = "asset.png";

const buffer = await fs.readFile(assetImagePath);
let file = createGenericFile(buffer, assetImagePath, {
  contentType: "image/png",
});

// upload new image and get image uri
const [image] = await umi.uploader.upload([file]);
console.log("image uri:", image);

const metadata = {
  name: "My Updated Asset",
  description: "My Updated Asset Description",
  image,
  external_url: "https://example.com",
  attributes: [
    {
      trait_type: "trait1",
      value: "value1",
    },
    {
      trait_type: "trait2",
      value: "value2",
    },
  ],
  properties: {
    files: [
      {
        uri: image,
        type: "image/jpeg",
      },
    ],
    category: "image",
  },
};

// upload offchain json using irys and get metadata uri
const uri = await umi.uploader.uploadJson(metadata);
console.log("Asset offchain metadata URI:", uri);

// Fetch the accounts using the address
const asset = await fetchAsset(umi, UMIPublicKey("YOUR_ASSET_ADDRESS_HERE"));
const collection = await fetchCollection(
  umi,
  UMIPublicKey("YOUR_COLLECTION_ADDRESS_HERE"),
);

await update(umi, {
  asset,
  collection,
  name: "My Updated Asset",
  uri,
}).sendAndConfirm(umi);

let explorerLink = getExplorerLink("address", asset.publicKey, "devnet");
console.log(`Asset updated with new metadata URI: ${explorerLink}`);

console.log("✅ Finished successfully!");

Run npx esrun update-metaplex-core-asset.ts. You should see something like:

% npx esrun update-metaplex-core-asset.ts
Loaded user: 2YkGRHjwD3jqcu4ie6pL9Axpdx5AKa6KDyj8bF473Vk5
image uri: https://arweave.net/DtdF6YbCbSV6y5eeet6Hk2oJq2afFwKzZmrLpfFkyLym
Asset offchain metadata URI: https://gateway.irys.xyz/DQysfQZ9CuGveSYDWKZwhjUX7VnRSzfaPtvojo44rhJw
Asset updated with new metadata URI: https://explorer.solana.com/address/BXfRBtgVRmEnwQaLqCAproeuSMNdkgWYptHvjvHekHht?cluster=devnet
✅ Finished successfully!

Inspect the updated NFT on Solana Explorer!

Congratulations! You've successfully learned how to use the Metaplex mpl-core SDK to create, update, and add an Asset to a Collection. That's everything you need to build out your own collection for just about any use case. You could build a new event ticketing platform, revamp a retail business membership program, or even digitize your school's student ID system. The possibilities are endless!

Challenge

The steps covered above for creating an NFT would be incredibly tedious to execute for thousands of NFTs in one go. Many providers, including Metaplex, Magic Eden, and Tensor have so-called 'fair launch' tools that take care of minting large quantities of NFTs and ensuring they are sold within the parameters set by their creators. Dive into how Metaplex support fair launches through Candy Machine!

Completed the lab?

Push your code to GitHub and tell us what you thought of this lesson! // TODO

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