typo

gradual.tex

@@ -5,7 +5,7 @@ flexibility of dynamic typing. The idea is to introduce an \emph{unknown}
 some static type-checking can be omitted, at the cost of some additional
 runtime checks. The use of both static typing and dynamic typing in a same
 program creates a boundary between the two, where the compiler automatically
-adds ---often costly~\cite{takikawa2016sound}--- dynamic type-checks to ensure 
+adds---often costly~\cite{takikawa2016sound}---dynamic type-checks to ensure 
 that a value crossing the barrier is correctly typed.
 
 Occurrence typing and gradual typing are two complementary disciplines