http://dswarmsikhttkg7jgsoyfiqpj3ighupfrvuz5ri3lu5q2dlqyrpgk7ad.onion/notes/lsg.html
Showing \(p\to q\) using the rule \(\to i\) is now called type checking , an topic in the construction of compilers for typed programming languages. (Huth, Michael and Ryan, Mark, 2004) Formulate the rule \(\to i\) as: Note that the line immediately following a closed box has to match the pattern of the conclusion of the rule that uses the box.