Mathematics Department, Tulane University, New Orleans, Louisiana, USA. bcummins@tulane.edu|Mathematics Department, Tulane University, New Orleans, Louisiana, USA. bcummins@tulane.edu|Mathematics Department, Tulane University, New Orleans, Louisiana, USA. bcummins@tulane.edu|Mathematics Department, Tulane University, New Orleans, Louisiana, USA. bcummins@tulane.edu|Mathematics Department, Tulane University, New Orleans, Louisiana, USA. bcummins@tulane.edu