text: =PA3), 1. Introduction. 
  
  203. Haaparanta 2009, pp. 4–6 (https://books.google.com/books?id=0jXavKsArnIC&pg=PA4); 
  
  Hintikka & Spade, Modern logic, Logic since 1900. 
  
  204. Ewald 2019. 
  205. Ewald 2019; Schreiner 2021, p. 22. 