User blog comment:Ubersketch/CNF in my FSS definition/@comment-35470197-20190808221731/@comment-35470197-20190809002703

The existence of the base case is irrelevant to the circular logic on the domain of functions. See this.

To begin with, declare the domain of "all" functions which you use before applying them to some terms. Then you will find the actual circular logic, if you understand the definition of a function includes its domain.