One and one is two, unless you're an accountant or an official with any department of revenue. I saw this summary of a recent NY case on CCH (Ilyaich, New York Division of Tax Appeals, Administrative Law Judge Unit, DTA No. 820875, October 18, 2007).
"A taxpayer was entitled to claim head of household filing status, for New York personal income tax purposes, despite being legally married during the years in question. The taxpayer met the requirements under IRC Sec. 7703(b) to be considered unmarried for the years in question because she: (1) did not live with her husband; (2) solely and individually maintained an apartment that was the principal place of abode for her minor children; and (3) was otherwise entitled to claim a deduction for a personal exemption for her minor children."