docs: rename proof rule subst -> cut

docs/base-logic.tex

@@ -203,7 +203,7 @@ This is entirely standard.
   {}
   {\prop \proves \prop}
 \and
-\infer[Subst]
+\infer[Cut]
   {\prop \proves \propB \and \propB \proves \propC}
   {\prop \proves \propC}
 \and