Improve documentation clarity

Author: TGWDB

doc/cprover-manual/api.md

@@ -132,9 +132,10 @@ the array **dest** with the given value.
 __CPROVER_bool __CPROVER_enum_is_in_range();
 ```
 
-The function **\_\_CPROVER\_enum\_is\_in\_range** returns true
-if their one argument (an `enum`) is one of the defined values for
-the enumeration. For example
+The function **\_\_CPROVER\_enum\_is\_in\_range** is used to check
+that an enumeration has one of the defined enumeration values. In
+the following example `__CPROVER_enum_is_in_range(ev1)` will return
+true and the assertion will pass
 ```C
 enum my_enum { first, second };
 
@@ -144,7 +145,7 @@ int main()
   assert(__CPROVER_enum_is_in_range(ev1));
 }
 ```
-would return true, while the following example
+However, in the example below the assertion will fail
 ```C
 enum my_enum { first, second };
 
@@ -154,7 +155,7 @@ int main()
   assert(__CPROVER_enum_is_in_range(ev1));
 }
 ```
-would return false.
+
 
 #### Uninterpreted Functions