Ruback (1986) has argued that the present value to a corporation of a riskless taxable cash inflow should be calculated by discounting the riskless after-tax cash flow by the riskless corporate after-tax (borrowing) interest rate. A cash flow is defined as riskless when the realisation of the cash flow is certain, does not depend on the actions of the owner of the cash flow, and does not depend of the identity of the owner.