Better preimages stats docs

Author: davxy

preimages/README.md

@@ -5,12 +5,12 @@ and this subsystem STF specific [schema](./preimages.asn).
 
 ## Statistics
 
-A subset of `ServiceActivityRecord` structure is updated by the STF involved
-processing these test vectors.
+A subset of service activity statistics ($π_S$) updated by the STF subsystem used
+to process these test vectors.
 
-In particular the `provided-count` and `provided-size` items are updated
-when new preimages are provided to be included in the chain storage via the
-extrinsic.
+In particular the `provided-count` (p.0) and `provided-size` (p.1) items are
+updated when new preimages are provided to be included in the chain storage via
+the extrinsic.
 
 ## Vectors
 

preimages/preimages.asn

@@ -36,16 +36,17 @@ AccountsMapEntry ::= SEQUENCE {
 }
 
 State ::= SEQUENCE {
-	-- Relevant services account data [δ]. Refer to T(σ) in GP Appendix D.
+	-- [δ] Relevant services account data. Refer to T(σ) in GP Appendix D.
     accounts SEQUENCE OF AccountsMapEntry,
-    -- Statistics updated by the preimages STF subsystem.
+	-- [π_S] Services statistics.
+	-- Note: Only stats related to preimages STF are updated, in particular:
+	-- provided_count (p.0), provided_size (p.1).
     statistics ServicesStatistics
 }
 
 Input ::= SEQUENCE {
     -- [E_P] Preimages extrinsic.
     preimages PreimagesExtrinsic,
-
     -- [H_t] Block's timeslot.
     slot TimeSlot
 }

statistics/README.md

@@ -10,7 +10,7 @@ These vectors exclusively contribute to updating validator-related statistics
 
 In contrast, service and core statistics ($π_S$ and $π_C$) are updated by
 vectors that more directly influence the state changes relevant to those
-metrics (i.e. see `preimages`, `reports` and `accumulate`).
+metrics (i.e. see [preimages](../preimages/README.md#statistics), `reports` and `accumulate`).
 
 ## ⚠️Extrinsic Semantic Validity