P/E multiple + cost of debt/ accretion/dilution

Given a P/E of 10x, (1) what cost of debt is the minimum a company could use to accretively repurchase shares? (2) What about before tax cost of debt?

Would this be the correct way to think of it:

(1) seller's yield = inverse of P/E multiple = 1/10 = 10%; so would need cost of debt to be less than 10%

(2) would need cost of debt to be 10%(1-tax rate).