Detroit is a creature of the state of Michigan. The state constitution trumps any other law or charter that's in effect [[Although even Detroit's city charter guarantees the pensions as well). If Detroit claims insolvency, the money to pay for the pensions can't be pulled out of its rear end. The liability would be shifted to the state of Michigan, even if the pensioners sued the city of Detroit.
There is a reason, after all, why the state of Michigan is doing everything to prevent a Detroit bankruptcy, besides the legal costs.
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