From ccd6ac4d44b5c91aa2d1c2534c7be57963b616d5 Mon Sep 17 00:00:00 2001
From: Wilfred Hughes <me@wilfred.me.uk>
Date: Sun, 21 Mar 2021 13:34:01 -0700
Subject: Add notes on LCS weaknesses

---
 text_diff_notes.md | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 text_diff_notes.md

diff --git a/text_diff_notes.md b/text_diff_notes.md
new file mode 100644
index 000000000..c4a183dea
--- /dev/null
+++ b/text_diff_notes.md
@@ -0,0 +1,48 @@
+Consider changing:
+
+```
+foo();
+bar();
+```
+
+To:
+
+```
+if (true) {
+  foo();
+}
+```
+
+What we want:
+
+```
++ if (true) {
+   foo();
+-  bar();
++ }
+```
+
+A longest-common-subsequence algorithm is wrong here. The longest
+subsequence is five tokens:
+
+```
+( ) ( ) ;
+```
+
+which leads to:
+
+```
++if+ (+true+) +{+
+   +foo+();
+    -bar-();
++}+
+```
+
+so we claim `foo` is added. We want the following *four* tokens to be
+preserved:
+
+```
+foo ( ) ;
+```
+
+Proposed solution: advance on both sides, keep first match.
-- 
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