add an interface folder that lists common interfaces

contracts/interfaces/ERC1155.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../token/ERC1155/IERC1155.sol";
+import "../token/ERC1155/IERC1155MetadataURI.sol";
+import "../token/ERC1155/IERC1155Receiver.sol";

contracts/interfaces/ERC1271.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+interface IERC1271
+{
+    function isValidSignature(bytes calldata data, bytes calldata signature) external view returns (bytes4 magicValue);
+}

contracts/interfaces/ERC1363.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../token/ERC20/IERC20.sol";
+import "../introspection/IERC165.sol";
+
+interface IERC1363 is IERC20, IERC165 {
+  /*
+   * Note: the ERC-165 identifier for this interface is 0x4bbee2df.
+   * 0x4bbee2df ===
+   *   bytes4(keccak256('transferAndCall(address,uint256)')) ^
+   *   bytes4(keccak256('transferAndCall(address,uint256,bytes)')) ^
+   *   bytes4(keccak256('transferFromAndCall(address,address,uint256)')) ^
+   *   bytes4(keccak256('transferFromAndCall(address,address,uint256,bytes)'))
+   */
+
+  /*
+   * Note: the ERC-165 identifier for this interface is 0xfb9ec8ce.
+   * 0xfb9ec8ce ===
+   *   bytes4(keccak256('approveAndCall(address,uint256)')) ^
+   *   bytes4(keccak256('approveAndCall(address,uint256,bytes)'))
+   */
+
+  /**
+   * @notice Transfer tokens from `msg.sender` to another address and then call `onTransferReceived` on receiver
+   * @param to address The address which you want to transfer to
+   * @param value uint256 The amount of tokens to be transferred
+   * @return true unless throwing
+   */
+  function transferAndCall(address to, uint256 value) external returns (bool);
+
+  /**
+   * @notice Transfer tokens from `msg.sender` to another address and then call `onTransferReceived` on receiver
+   * @param to address The address which you want to transfer to
+   * @param value uint256 The amount of tokens to be transferred
+   * @param data bytes Additional data with no specified format, sent in call to `to`
+   * @return true unless throwing
+   */
+  function transferAndCall(address to, uint256 value, bytes memory data) external returns (bool);
+
+  /**
+   * @notice Transfer tokens from one address to another and then call `onTransferReceived` on receiver
+   * @param from address The address which you want to send tokens from
+   * @param to address The address which you want to transfer to
+   * @param value uint256 The amount of tokens to be transferred
+   * @return true unless throwing
+   */
+  function transferFromAndCall(address from, address to, uint256 value) external returns (bool);
+
+
+  /**
+   * @notice Transfer tokens from one address to another and then call `onTransferReceived` on receiver
+   * @param from address The address which you want to send tokens from
+   * @param to address The address which you want to transfer to
+   * @param value uint256 The amount of tokens to be transferred
+   * @param data bytes Additional data with no specified format, sent in call to `to`
+   * @return true unless throwing
+   */
+  function transferFromAndCall(address from, address to, uint256 value, bytes memory data) external returns (bool);
+
+  /**
+   * @notice Approve the passed address to spend the specified amount of tokens on behalf of msg.sender
+   * and then call `onApprovalReceived` on spender.
+   * @param spender address The address which will spend the funds
+   * @param value uint256 The amount of tokens to be spent
+   */
+  function approveAndCall(address spender, uint256 value) external returns (bool);
+
+  /**
+   * @notice Approve the passed address to spend the specified amount of tokens on behalf of msg.sender
+   * and then call `onApprovalReceived` on spender.
+   * @param spender address The address which will spend the funds
+   * @param value uint256 The amount of tokens to be spent
+   * @param data bytes Additional data with no specified format, sent in call to `spender`
+   */
+  function approveAndCall(address spender, uint256 value, bytes memory data) external returns (bool);
+}
+
+interface IERC1363Receiver {
+  /*
+   * Note: the ERC-165 identifier for this interface is 0x88a7ca5c.
+   * 0x88a7ca5c === bytes4(keccak256("onTransferReceived(address,address,uint256,bytes)"))
+   */
+
+  /**
+   * @notice Handle the receipt of ERC1363 tokens
+   * @dev Any ERC1363 smart contract calls this function on the recipient
+   * after a `transfer` or a `transferFrom`. This function MAY throw to revert and reject the
+   * transfer. Return of other than the magic value MUST result in the
+   * transaction being reverted.
+   * Note: the token contract address is always the message sender.
+   * @param operator address The address which called `transferAndCall` or `transferFromAndCall` function
+   * @param from address The address which are token transferred from
+   * @param value uint256 The amount of tokens transferred
+   * @param data bytes Additional data with no specified format
+   * @return `bytes4(keccak256("onTransferReceived(address,address,uint256,bytes)"))`
+   *  unless throwing
+   */
+  function onTransferReceived(address operator, address from, uint256 value, bytes memory data) external returns (bytes4);
+}
+
+interface IERC1363Spender {
+  /*
+   * Note: the ERC-165 identifier for this interface is 0x7b04a2d0.
+   * 0x7b04a2d0 === bytes4(keccak256("onApprovalReceived(address,uint256,bytes)"))
+   */
+
+  /**
+   * @notice Handle the approval of ERC1363 tokens
+   * @dev Any ERC1363 smart contract calls this function on the recipient
+   * after an `approve`. This function MAY throw to revert and reject the
+   * approval. Return of other than the magic value MUST result in the
+   * transaction being reverted.
+   * Note: the token contract address is always the message sender.
+   * @param owner address The address which called `approveAndCall` function
+   * @param value uint256 The amount of tokens to be spent
+   * @param data bytes Additional data with no specified format
+   * @return `bytes4(keccak256("onApprovalReceived(address,uint256,bytes)"))`
+   *  unless throwing
+   */
+  function onApprovalReceived(address owner, uint256 value, bytes memory data) external returns (bytes4);
+}

contracts/interfaces/ERC165.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../introspection/IERC165.sol";

contracts/interfaces/ERC173.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../introspection/IERC165.sol";
+
+interface IERC173 is IERC165 {
+    /// @dev This emits when ownership of a contract changes.
+    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
+
+    /// @notice Get the address of the owner
+    /// @return The address of the owner.
+    function owner() view external returns(address);
+
+    /// @notice Set the address of the new owner of the contract
+    /// @dev Set _newOwner to address(0) to renounce any ownership.
+    /// @param _newOwner The address of the new owner of the contract
+    function transferOwnership(address _newOwner) external;
+}

contracts/interfaces/ERC1820.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../introspection/IERC1820Implementer.sol";
+import "../introspection/IERC1820Registry.sol";

contracts/interfaces/ERC20.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../token/ERC20/IERC20.sol";

contracts/interfaces/ERC2612.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../drafts/IERC20Permit.sol";
+
+interface IERC2612 is IERC20Permit {}

contracts/interfaces/ERC3156.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+interface IERC3156FlashLender {
+    /**
+     * @dev The amount of currency available to be lent.
+     * @param token The loan currency.
+     * @return The amount of `token` that can be borrowed.
+     */
+    function maxFlashLoan(
+        address token
+    ) external view returns (uint256);
+
+    /**
+     * @dev The fee to be charged for a given loan.
+     * @param token The loan currency.
+     * @param amount The amount of tokens lent.
+     * @return The amount of `token` to be charged for the loan, on top of the returned principal.
+     */
+    function flashFee(
+        address token,
+        uint256 amount
+    ) external view returns (uint256);
+
+    /**
+     * @dev Initiate a flash loan.
+     * @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
+     * @param token The loan currency.
+     * @param amount The amount of tokens lent.
+     * @param data Arbitrary data structure, intended to contain user-defined parameters.
+     */
+    function flashLoan(
+        address receiver,
+        address token,
+        uint256 amount,
+        bytes calldata data
+    ) external returns (bool);
+}
+
+interface IERC3156FlashBorrower {
+    /**
+     * @dev Receive a flash loan.
+     * @param initiator The initiator of the loan.
+     * @param token The loan currency.
+     * @param amount The amount of tokens lent.
+     * @param fee The additional amount of tokens to repay.
+     * @param data Arbitrary data structure, intended to contain user-defined parameters.
+     * @return The keccak256 hash of "ERC3156FlashBorrower.onFlashLoan"
+     */
+    function onFlashLoan(
+        address initiator,
+        address token,
+        uint256 amount,
+        uint256 fee,
+        bytes calldata data
+    ) external returns (bytes32);
+}

contracts/interfaces/ERC721.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../token/ERC721/IERC721.sol";
+import "../token/ERC721/IERC721Enumerable.sol";
+import "../token/ERC721/IERC721Metadata.sol";
+import "../token/ERC721/IERC721Receiver.sol";

contracts/interfaces/ERC725.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+interface IERC725
+{
+    event DataChanged(bytes32 indexed key, bytes32 indexed value);
+    event ContractCreated(address indexed contractAddress);
+
+    function getData(bytes32 key) external view returns (bytes32 value);
+    function setData(bytes32 key, bytes32 value) external;
+    function execute(uint256 operationType, address to, uint256 value, bytes calldata _data) external;
+}

contracts/interfaces/ERC777.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../token/ERC777/IERC777.sol";
+import "../token/ERC777/IERC777Recipient.sol";
+import "../token/ERC777/IERC777Sender.sol";