Update doc/cprover-manual/requires-and-ensures-clauses.md

Co-authored-by: Saswat Padhi <[email protected]>

Author: feliperodri

doc/cprover-manual/requires-and-ensures-clauses.md

@@ -35,7 +35,7 @@ side effects (i.e., do not modify any local or global state). This will be check
 
 ### Semantics
 
-The semantics of a _requires_ clause *r* of a given function *f* can be
+The semantics of _ensures_ and _requires_ clauses can be
 understood in two contexts: enforcement and replacement. 
 To illustrate these two perspectives, consider the following implementation of the `sum` function.