 As Church has emphasized (e.g., 1956: 59), metamathematical treatment of schemas requires use of formalized or logically perfect languages and an axiomatized theory of strings as found for the first time in Tarski’s 1933 truth-definition paper (1933/1983: 152–256). For more on the history, philosophy, and mathematics of this important but somewhat neglected field, see Corcoran et al. 1974; Corcoran 2006).