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29/**
30 * @notice Transfers `amount` tokens from `from` to `to`
31 * @param from Address to transfer tokens from
32 * @param to Address to transfer tokens to
33 * @param amount Amount of tokens to transfer
34 * @return True if the transfer was successful, reverts otherwise
35 * @dev The caller must have allowance for `from`'s tokens of at least `amount`
36 */
37function transferFrom(address from, address to, uint256 amount) external virtual override returns (bool) {
38    _spendAllowance(from, _msgSender(), amount);
39    _beforeTokenTransfer(from, to, amount);
40
41    return _transferFrom(from, to, amount);
42}
43
44function _transferFrom(address from, address to, uint256 amount) internal virtual returns (bool) {
45    if (from == address(0)) {
46        revert ERC20InvalidSender(address(0));
47    }
48    if (to == address(0)) {
49        revert ERC20InvalidReceiver(address(0));
50    }
51
52    _writeTransfer(from, to, amount);
53
54    emit Transfer(from, to, amount);
55    return true;
56}