What is the primary difference between an in-state 4.2% YTM Revenue Municipal Bond, a 2.65% YTM U.S. T-Note, and a BB-Rated 6.72% YTM Corporate Debenture (assuming each has 8 years to maturity and Muni uses a tax-equivalent yield) in terms of tax treatment of coupon interest and default risk (how each is collateralized)...assuming a marginal tax rate of 28%?