Editing Laws of Form (section)

{{Short description|1969 non-fiction book by G. Spencer-Brown}}
{{Use dmy dates|date=January 2020}}
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'''''Laws of Form''''' (hereinafter '''''LoF''''') is a book by [[G. Spencer-Brown]], published in 1969, that straddles the boundary between [[mathematics]] and [[philosophy]]. ''LoF'' describes three distinct [[logical system]]s:
* The '''primary arithmetic''' (described in Chapter 4 of ''LoF''), whose models include [[Two-element Boolean algebra#Some basic identities|Boolean arithmetic]];
* The '''primary algebra''' (Chapter 6 of ''LoF''), whose [[interpretation (logic)|models]] include the [[two-element Boolean algebra]] (hereinafter abbreviated '''2'''), [[Boolean logic]], and the classical [[propositional calculus]];
* '''Equations of the second degree''' (Chapter 11), whose [[interpretation (logic)|interpretations]] include [[finite automata]] and [[Alonzo Church]]'s Restricted Recursive Arithmetic (RRA).

"Boundary algebra" is a {{harvp|Meguire|2011}} term for the union of the primary algebra and the primary arithmetic. ''Laws of Form'' sometimes loosely refers to the "primary algebra" as well as to ''LoF''.