 In effect the class variables can be seen as propositional function variables, restricted to r-types in which only predicative functions appear, in arguments as well, leading to what might be seen as “hereditarily predicative functions”. In other words, the class variables can be replaced with propositional function variables in which the r-type of the function, and of all the arguments are of the form \((\beta_1, \beta_2, \ldots, \beta_m )/1\) and the same applies to \(\beta_1, \beta_2, \ldots, \beta_m\) as well. This means that variables and terms for classes will obey the simple theory of types. These can be contrasted with r-types by presenting an alternative system of simple types or “s-types”.