I will explain basic concepts/problems of complex analysis in infinite dimensions, and survey the few approaches that are available to solve those problems.
@incollection{JEDP_1998____A8_0, author = {Lempert, L\'aszl\'o}, title = {The {Cauchy-Riemann} equations in infinite dimensions}, booktitle = {}, series = {Journ\'ees \'equations aux d\'eriv\'ees partielles}, eid = {8}, pages = {1--8}, publisher = {Universit\'e de Nantes}, year = {1998}, mrnumber = {99k:46081}, zbl = {01808717}, language = {en}, url = {http://www.numdam.org/item/JEDP_1998____A8_0/} }
Lempert, László. The Cauchy-Riemann equations in infinite dimensions. Journées équations aux dérivées partielles (1998), article no. 8, 8 p. http://www.numdam.org/item/JEDP_1998____A8_0/
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