Abstract
The new idea of flip invariance of action functionals in multidimensional lattices was recently highlighted as a key feature of discrete integrable systems. Flip invariance was proved for several particular cases of integrable quad-equations by Bazhanov, Mangazeev and Sergeev and by Lobb and Nijhoff. We provide a simple and case-independent proof for all integrable quad-equations. Moreover, we find a new relation for Lagrangians within one elementary quadrilateral which seems to be a fundamental building block of the various versions of flip invariance.
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A.I. Bobenko was partially supported by the DFG Research Unit “Polyhedral Surfaces”.
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Bobenko, A.I., Suris, Y.B. On the Lagrangian Structure of Integrable Quad-Equations. Lett Math Phys 92, 17–31 (2010). https://doi.org/10.1007/s11005-010-0381-9
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DOI: https://doi.org/10.1007/s11005-010-0381-9