http://dswarmsikhttkg7jgsoyfiqpj3ighupfrvuz5ri3lu5q2dlqyrpgk7ad.onion/notes/lsg.html
Second-order logic Some terms for the language of second-order logic: ( https://plato.stanford.edu/entries/frege-theorem/#S1 ) object names: \(a, b, \dots\) objects variables: \(x, y, \dots\) n -place relation names: \(P^{n}, Q^{n}, \ldots \ \ \ (n\geq1)\) n -place relation variables: \(F^{n}, G^{n}, \ldots \ \ \ (n\geq1)\) Explanations: Object names and variables denote a domain of objects; n -place relation names and variables denote a domain of n -place relations;...