https://www.econstor.eu/handle/10419/257729
EconStor: A quasi-closed-form solution for the valuation of American put options
EconStor is a publication server for scholarly economic literature, provided as a non-commercial public service by the ZBW.
closed form solution
https://www.wolframalpha.com/input/?i=closed-form+solution
closed-form solution - Wolfram|Alpha
closed form solutionwolframalpha