Title: Reversible temperature exchange upon thermal contact,
Abstract: According to a well-known principle of thermodynamics, the transfer of heat
between two bodies is reversible when their temperatures are infinitesimally
close. As we demonstrate, a little-known alternative exists: two bodies with
temperatures different by an arbitrary amount can completely exchange their
temperatures in a reversible way if split into infinitesimal parts that are
brought into thermal contact sequentially.