Early in the first presidential debate, Mitt Romney said his across-the-board tax cuts will not add to the deficit. He also said he would not reduce the "share" of taxes paid by higher-income Americans. Romney's tax plan has been widely criticized for pledging to close the deficit while steeply lowering tax rates, which many economists say is mathematically impossible without raising the tax burden on the middle class by closing popular loopholes and deductions. Obama rejected Romney's claim, saying, "It's math. It's arithmetic." Here, some reactions from the Twitterverse: