diff --git a/src/old.clj b/src/old.clj
index 7f30ae6..222087c 100644
--- a/src/old.clj
+++ b/src/old.clj
@@ -520,7 +520,7 @@
         scopes* (conj scopes (new-scope))
         env* (merge env (unification->env unif symtable-ref scopes*))]
     (expand (transcribe (:template rule) env* @symtable-ref scopes*)
-            env ;; 아마도 `env*`를 써야 되고 `env`를 안 써야 될까?
+            env ;; 아마도 `env*`를 써야 되고 `env`를 안 써야 된가?
             symtable-ref
             scopes)))
 
diff --git a/src/r7rs.ebnf b/src/r7rs.ebnf
index 14dd8ce..e0e1a44 100644
--- a/src/r7rs.ebnf
+++ b/src/r7rs.ebnf
@@ -3,11 +3,17 @@ program = <intertoken-space> datum*
 (* tokens *)
 boolean = #"#(t(rue)?|f(alse)?)" <intertoken-space>
 semicolon = ';'
+left-paren = '(' <intertoken-space>
+right-paren = ')' <intertoken-space>
 
 (* datum *)
-datum = simple-datum
+<datum> = simple-datum
 
-<simple-datum> = boolean
+<simple-datum> = boolean | symbol
+
+(* symbol *)
+symbol = ordinary-symbol
+<ordinary-symbol> = #"[\P{Lu}\P{Ll}\P{Lt}\P{Lm}\P{Lo}\P{Nl}\P{No}\P{Pd}\P{Pc}\P{Sc}\P{Po}\P{Sm}\P{Sk}\P{So}\P{Co}\u200c\u200d&&[^;|\".,#]][\P{Lu}\P{Ll}\P{Lt}\P{Lm}\P{Lo}\P{Nl}\P{No}\P{Pd}\P{Pc}\P{Sc}\P{Po}\P{Sm}\P{Sk}\P{So}\P{Co}\u200c\u200d\P{Nd}\P{Me}\P{Mc}.&&[^;|\",#]]*"
 
 (* atmosphere *)
 atmosphere = whitespace | comment | directive