@article {zbMATH06132858, title = {First variation formula for discrete variational problems in two independent variables.}, journal = {Rev. R. Acad. Cienc. Exactas F{\'\i}s. Nat., Ser. A Mat., RACSAM}, volume = {106}, number = {1}, year = {2012}, note = {

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}, pages = {111{\textendash}135}, publisher = {Springer, Milan; Real Academia de Ciencias Exactas, F\'{\i}sicas y Naturales, Madrid}, abstract = {

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}, issn = {1578-7303; 1579-1505/e}, doi = {10.1007/s13398-011-0034-6}, author = {Ana Cristina {Casimiro} and C{\'e}sar {Rodrigo}} }