🌐EnglishEnglishDeutschEspañolFrançaisItalianoNederlandsPortuguêsSvenskaРусскийالعربيةفارسی한국어中文日本語EntityQ944238· pop 20· linked from 161 articlesParseval's identitymathematical conceptAvailable in 20 languagesEspañolFrançaisDeutsch中文日本語РусскийPortuguêsItalianoالعربيةCatalanConnectionsinner product spaceEntityLp spaceEntityCategoriesFourier seriesTheorems in functional analysis