Tweak wording around provider purity

Author: camelid

src/queries/query-evaluation-model-in-detail.md

@@ -38,10 +38,10 @@ corresponding result. However, we have to apply some restrictions in order for
 this to be sound:
 
  - The key and result must be immutable values.
- - The provider function must be a pure function, that is, for the same key it
-   must always yield the same result.
+ - The provider function must be a pure function in the sense that for the same
+   key it must always yield the same result.
  - The only parameters a provider function takes are the key and a reference to
-   the "query context" (which provides access to rest of the "database").
+   the "query context" (which provides access to the rest of the "database").
 
 The database is built up lazily by invoking queries. The query providers will
 invoke other queries, for which the result is either already cached or computed