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diff --git a/73.md b/73.md
index 7fb9a3c..3e975ae 100644
--- a/73.md
+++ b/73.md
@@ -18,6 +18,7 @@ There are certain established global content identifiers such as [Book ISBNs](ht
 | URLs                   | "`<URL, normalized, no fragment>`"                         | "web"                    |
 | Books                  | "isbn:`<id, without hyphens>`"                             | "isbn"                   |
 | Geohashes              | "geo:`<geohash, lowercase>`"                               | "geo"                    |
+| Countries              | "iso3166:`<code, uppercase>`"                              | "iso3166"                |
 | Movies                 | "isan:`<id, without version part>`"                        | "isan"                   |
 | Papers                 | "doi:`<id, lowercase>`"                                    | "doi"                    |
 | Hashtags               | "#`<topic, lowercase>`"                                    | "#"                      |
@@ -43,6 +44,21 @@ For the webpage "https://myblog.example.com/post/2012-03-27/hello-world" the "i"
 ]
 ```
 
+### Geohashes:
+
+- Geohash: `["i", "geo:ezs42e44yx96"]` - https://www.movable-type.co.uk/scripts/geohash.html
+
+Geohashes are a geocoding system that encodes geographic locations into short strings of letters and digits. They MUST be lowercase.
+
+### Countries:
+
+ISO 3166 codes can reference countries (ISO 3166-1 alpha-2) or subdivisions like states/provinces (ISO 3166-2).
+
+- Country (Venezuela): `["i", "iso3166:VE"]`
+- Subdivision (California, USA): `["i", "iso3166:US-CA"]`
+
+ISO 3166 codes MUST be uppercase. More info: https://en.wikipedia.org/wiki/ISO_3166
+
 ### Books:
 
 - Book ISBN: `["i", "isbn:9780765382030"]` - https://isbnsearch.org/isbn/9780765382030