In the 20th century, various Austrians incorporated models and mathematics into their analysis. Austrian economist Steven Horwitz argued in 2000 that Austrian methodology is consistent with macroeconomics and that Austrian macroeconomics can be expressed in terms of microeconomic foundations. Austrian economist Roger Garrison writes that Austrian macroeconomic theory can be correctly expressed in terms of diagrammatic models. In 1944, Austrian economist Oskar Morgenstern presented a rigorous schematization of an ordinal utility function (the Von Neumann–Morgenstern utility theorem) in "Theory of Games and Economic Behavior".