The Vilna Gaon and the Tzemach Tzedek Wrestle Over the Yarmulka

Source Sheet (https://rabbikraz.com/Yarmulka) - Stories from the Gemara about head covering - Does the Gemara's reference to head covering refer to a Yarmulka or to something more? - Is wearing a Yarmulka an obligation or "Midas Chassidus"? - Does it depend where you are or what you're doing? - Does covering your head with your hand work? - Drama over the Teshuva of the Tzemach Tzedek