update example trait name

Author: lcnr

book/src/recursive.md

@@ -35,7 +35,7 @@ impl A for i32 { }
 which results in program clauses like:
 
 ```notrust
-forall<T> { Implemented(Vec<T>: A) :- Implemented(T: MyTrait) }
+forall<T> { Implemented(Vec<T>: A) :- Implemented(T: A) }
 Implemented(u32: A)
 Implemented(i32: A)
 ```
@@ -94,4 +94,4 @@ The [SLG solver] in contrast starts by exploring `?X = u32` and finds
 that it works, and then later tries to explore `?X = i32` and finds that it
 fails (because `i32: B` is not true).
 
-[SLG solver]: ./engine.md
+[SLG solver]: ./engine.md