On reflection principles (Q5896339)

The paper contains some minor refinements on the topic of its title mainly of the literature in the 60's [in particular: \textit{S. Feferman}, Fundam. Math. 49, 35-92 (1960; Zbl 0095.243)]. It is not up-to-date because it neglects to specify the data, that is, formal rules, which determine a formal system, and a fortiori neglects to use the notion of canonical representation of those data w.r.t. the system(s) considered.