fix typos

chapter1.md

@@ -12,7 +12,7 @@
 
 ## Strict vs. Lazy Evaluation
 - strict languages: the arguments to a function are evaluated before the body of the function;
-lazy languages: arguments are evaluated in a demand-driven fashion; they are initially passed in unevaluated form and are evaluated only when (and if!) the computation needs the results to continue; once a given argument is evaluated, the value of that argument is cached -> if it is ever needed again, it can be looked up rather than recomputed (this caching is known as *memoization*)
+  lazy languages: arguments are evaluated in a demand-driven fashion; they are initially passed in unevaluated form and are evaluated only when (and if!) the computation needs the results to continue; once a given argument is evaluated, the value of that argument is cached -> if it is ever needed again, it can be looked up rather than recomputed (this caching is known as *memoization*)
 
 - strict languages: can describe worst-case data structures, but not amortized ones;
 lazy languages: can describe amortized data structures, but not worst-case ones
@@ -25,4 +25,4 @@ lazy languages: can describe amortized data structures, but not worst-case ones
   3. **an object / a version:** an instance of a data type (such as particular list or tree)
   4. **a persistent identity:** a unique identity that is invariant under updates;
     different versions of the same data structure *share a common persistent identity*;
-    the persistent identity of an ephemeral data structure can be reified as a reference cell, but this approach is insufficient for modelling the persistent identity of a persistent data structure
+    the persistent identity of an ephemeral data structure can be reified as a reference cell, but this approach is insufficient for modelling the persistent identity of a persistent data structure