In 1880, Marxian economist Sergei Podolinsky attempted to theorize a labor theory of value based on embodied energy; his work was read and critiqued by Marx and Engels.[11] Otto Neurath developed an ecological approach based on a natural economy whilst employed by the Bavarian Soviet Republic in 1919. He argued that a market system failed to take into account the needs of future generations, and that a socialist economy required Calculation in kind, the tracking of all the different materials, rather than synthesising them into money as a general equivalent. In this he was criticised by neo liberal economists such as Ludwig von Mises and Freidrich Hayek in what became known as the socialist calculation debate.[12]