Situations as the one explained earlier, which are present in mature financial markets, cannot be modelled within the single-firm Merton model, but also not by its straightforward extensions to multiple firms with potentially correlated assets. To demonstrate this, consider two financial firms, formula_1, with limited liability, which both own system-exogenous assets of a value formula_2 at a maturity formula_3, and which both owe a single amount of zero coupon debt formula_4, due at time formula_5. "System-exogenous" here refers to the assumption, that the business asset formula_6 is not influenced by the firms in the considered financial system.