Clarify partition routing based on minimizer selection

The text clarifies how partition routing is independent of minimizer selection and details the hash-based calculation for the partition index.

theory-minimizer_selection.md

@@ -48,11 +48,10 @@ The choice of $s$ is not arbitrary. Low-complexity m-mers (homopolymers, short t
 
 If the minimum period length is found to be $m$ as observed in the above table, then the sequence is aperiodic, as no shorter period can be identified.
 
-## Partition routing is independent of minimizer selection
+## Partition routing
 
-The hash used to select a minimizer within a window (the minimum of several hash values) and the hash used to route a super-kmer to a storage partition are computed separately:
+A super-kmer's partition is the low $p$ bits of its minimizer's hash:
 
-- **Selection** uses $H$ applied to every candidate m-mer in the window, keeping the minimum.
+$$\text{partition} = H(\text{minimizer}) \bmod 2^p$$
-- **Partition routing** recomputes $H$ on the single selected minimizer only, once its position is fixed. This is a hash of one specific value, not the minimum of several, so it is uniformly distributed and safe to use directly for routing.
 
-See [Partitioning and indexing architecture](theory-indexing_architecture) for how the routing value is turned into a partition index.
+the same $H$ defined above, applied to the already-selected minimizer. See [Partitioning and indexing architecture](theory-indexing_architecture) for why $p$ is chosen well below $2m$ and how this keeps partitions balanced.