diff --git a/articles/scheme.md b/articles/scheme.md
index fc875f5..8c99e1b 100644
--- a/articles/scheme.md
+++ b/articles/scheme.md
@@ -13,6 +13,18 @@ work on R7RS began, splitting Scheme into two different (but still similar) lang
 a big language for practical use and a small, minimalistic version. Of course R7RS is still
 less bloated than [Common Lisp](common_lisp.md) and other mainstream languages.
 
+## Scheme Requests for Implementation (SRFI)
+Aside from the RnRS, Scheme is also informally standarized by the SRFI, in which extensions to Scheme are discussed, mainly
+libraries. Some SRFIs are:
+- [SRFI-13](https://srfi.schemers.org/srfi-13/srfi-13.html): adds string manipulation procedures
+- [SRFI-43](https://srfi.schemers.org/srfi-43/srfi-43.html)
+and [SRFI-133](https://srfi.schemers.org/srfi-133/srfi-133.html): both adding vector manipulation procedures
+- [SRFI-1](https://srfi.schemers.org/srfi-1/srfi-1.html): list library
+- [SRFI-125](https://srfi.schemers.org/srfi-125/srfi-125.html): hash tables
+- [SRFI-48](https://srfi.schemers.org/srfi-48/srfi-48.html): Common Lisp-like `format` procedure
+
+Unlike the revisions, these aren't hard requirements to implement, so Scheme implementations are free to implement them or not.
+
 ## Implementations
 Since Scheme (specially the R5RS standard) is simple, there are multiple implementations:
 - [CHICKEN Scheme](https://call-cc.org/): compiler and interpreter, supports extensions in a modular way,
@@ -24,6 +36,7 @@ called "eggs".
 - [Chibi Scheme](https://synthcode.com/scheme/chibi/): small implementation with a focus in being embeddable.
 - [Cyclone Scheme](https://justinethier.github.io/cyclone/): compiler, aims to support the R7RS standard.
 - [Gerbil Scheme](https://cons.io/)
+- [Gauche Scheme](https://practical-scheme.net/gauche/)
 - ...
 
 ## Examples
@@ -50,14 +63,16 @@ called "eggs".
 
 ## Resources
 - CHICKEN Scheme tutorials (of course most also applies to other implementations): <https://wiki.call-cc.org/tutorials>
+- <https://docs.scheme.org/>
 - [R5RS document](https://conservatory.scheme.org/schemers/Documents/Standards/R5RS/)
 - [Official Scheme site](https://www.scheme.org/)
-- A incomplete tutorial in wikibooks: <https://en.wikibooks.org/wiki/Scheme_Programming>
-- <https://try.scheme.org/>: Scheme in a web browser, seems to be Gambit Scheme.
-- <https://try.gambitscheme.org/>
-- <https://docs.scheme.org/>
 - [Teach Yourself Scheme in Fixnum Days](https://docs.scheme.org/tyscheme/)
 - [A Scheme Primer](https://files.spritely.institute/papers/scheme-primer.html)
+- [Practical Scheme](https://practical-scheme.net/)
 - [R7RS site](https://r7rs.org/)
+- <https://try.scheme.org/>: Scheme in a web browser, seems to be Gambit Scheme.
+- <https://try.gambitscheme.org/>: ditto
+- A incomplete tutorial in wikibooks: <https://en.wikibooks.org/wiki/Scheme_Programming>
+- List of SRFIs and which implementations implement each: <https://practical-scheme.net/wiliki/schemexref.cgi?SRFI>
 - The *CONS Should Not CONS Its Arguments, Part II: Cheney on the M.T.A.* paper,
 describes how to compile Scheme to C efficiently by using CPS.