docs/specification.md: note Process Update_Location_HLR
diff --git a/docs/specification.md b/docs/specification.md
index eb2f753..58ca1b5 100644
--- a/docs/specification.md
+++ b/docs/specification.md
@@ -3,6 +3,9 @@
Relevant specs:
* 3GPP TS 23.008: Organization of subscriber data
* Add pseudo IMSI and pseudo_imsi_i optionally to be saved in the HLR
+* "Process Update_Location_HLR" of TS 09.02
+ * Cancel location in old VLR/SGSN if IMSI pseudonymization is enabled, and a
+ previous pseudonymous IMSI exists for the subscriber
Optional additions we need to make, and where to make them: