fix a space

content/first-order-logic/syntax-and-semantics/main-operator.tex

@@ -71,7 +71,7 @@
 We call !!{formula}s by the names in \olref{tab:main-op} depending on
 which symbol their !!{main operator}
 is.\iftag{defNot,defOr,defAnd,defIf,defIff,defTrue,defFalse,defEx,defAll}
-{Recall, however, that defined operators do not officially appear in
+{ Recall, however, that defined operators do not officially appear in
 !!{formula}s. They are just abbreviations, so officially they cannot
 be the main operator of a formula. In proofs about all !!{formula}s
 they therefore do not have to be treated separately.}