ERC20approve.md

function approve(address spender, uint256 value) public returns (bool) {
  _approve(msg.sender, spender, value);
  return true;
}

function _approve(address owner, address spender, uint256 value) internal {
  require(owner != address(0), "ERC20: approve from the zero address");
  require(spender != address(0), "ERC20: approve to the zero address");
  _allowances[owner][spender] = value;
  emit Approval(owner, spender, value);
}