"A Fact Graph is a DAG, just like Excel." [1] A DAG won't work for everything! For example, the advance premium tax credit (i.e., the means-tested Obamacare health premium subsidy) has a circular relationship with the above-the-line deduction that self-employed people can take for healthcare costs. The IRS says you can iterate until you get stable values. [2]

[1] https://github.com/IRS-Public/direct-file/blob/main/direct-f... [2] https://www.irs.gov/pub/irs-drop/rp-14-41.pdf