Cartoon2D uses Boundary_SelectedGVs from the Boundary thorn, but it was missing from the interface.ccl. Since the function is defined implicitly, the compiler manages to figure it out at the linking stage. However, it should be added to the interface.

The associated pull request is here.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2649/missing-function-cartoon2d-interfaceccl