diff --git a/book/_toc.yml b/book/_toc.yml
index ba85f9d21d27d8feffe7f9ccbab6100f0fff5591..66ab5224241be9d7b1466eb6ec02eeff8f7b2b20 100644
--- a/book/_toc.yml
+++ b/book/_toc.yml
@@ -9,9 +9,6 @@ parts:
     chapters:
     - file: sandbox/blank
     - file: sandbox/robert
-    - file: sandbox/ObservationTheory/01_Introduction.md
-      sections:
-      - file: sandbox/ObservationTheory/02_Notebook_LeastSquares_dont_execute.ipynb
     - file: sandbox/prob/prob-intro
       title: Probability
       sections:
diff --git a/book/sandbox/SanPart/premath/00_03_PreMath.md b/book/sandbox/SanPart/premath/00_03_PreMath.md
index 27c0fc0be0fa1e7e5874def1a0e55233f9017fa3..80904533758a31e0e2f9bd0cb966cd0576b67490 100644
--- a/book/sandbox/SanPart/premath/00_03_PreMath.md
+++ b/book/sandbox/SanPart/premath/00_03_PreMath.md
@@ -1,3 +1,4 @@
+(PM_taylor)=
 # Taylor series
 
 ## Taylor's theorem for approximating functions of 1 variable