A previously unknown postcard from Einstein is among the notable items associated with Julio Rey Pastor, a key figure in modern Hispanic mathematics. The postcard is a unique piece of correspondence from the famous physicist. Further details about the postcard and its significance can be found through El País.

An image of the postcard, as well as a related letter signed by Einstein, is available for viewing. The postcard is part of a collection that includes other notable items, such as an fan dedicated by Ortega y Gasset, showcasing the connections and exchanges between Julio Rey Pastor and prominent thinkers of his time.