The company Joe works for has transferred him to Saudi Arabia to work on a two-year project. However, his spouse, Sandra, does not want to live in Saudi Arabia, so the couple, who have two small children, have agreed to live apart during those two years. Sandra, who is an attorney, is responsible for caring for their children and for most of the expenses associated with maintaining their household in Joe's absence. She decides to file a separate return. Assuming Joe and Sandra meet all the necessary criteria for taxpayers in their situation, what conclusion may the IRS make regarding their filing status?