 
                
                    
             Creative Commons Attribution 4.0 International license
                
    Creative Commons Attribution 4.0 International license
 
    In this work we propose a formal system for fuzzy algebraic reasoning. The sequent calculus we define is based on two kinds of propositions, capturing equality and existence of terms as members of a fuzzy set. We provide a sound semantics for this calculus and show that there is a notion of free model for any theory in this system, allowing us (with some restrictions) to recover models as Eilenberg-Moore algebras for some monad. We will also prove a completeness result: a formula is derivable from a given theory if and only if it is satisfied by all models of the theory. Finally, leveraging results by Milius and Urbat, we give HSP-like characterizations of subcategories of algebras which are categories of models of particular kinds of theories.
@InProceedings{castelnovo_et_al:LIPIcs.CSL.2022.13,
  author =	{Castelnovo, Davide and Miculan, Marino},
  title =	{{Fuzzy Algebraic Theories}},
  booktitle =	{30th EACSL Annual Conference on Computer Science Logic (CSL 2022)},
  pages =	{13:1--13:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-218-1},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{216},
  editor =	{Manea, Florin and Simpson, Alex},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2022.13},
  URN =		{urn:nbn:de:0030-drops-157332},
  doi =		{10.4230/LIPIcs.CSL.2022.13},
  annote =	{Keywords: categorical logic, fuzzy sets, algebraic reasoning, equational axiomatisations, monads, Eilenberg-Moore algebras}
}
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                     
                                                                                                            
                    