problem with latex macros in html

Makefile

@@ -26,8 +26,8 @@ all:  cours.pdf cours.html
 cours.pdf: 01_rappel.md 02_integrales.md 03_optimisation.md 04_edo.md 05_fourier.md 06_probas_stats.md 07_remerciements.md 08_notes.md
 	pandoc -s $(OPTIONS) $(PDFOPTIONS) -o $@ $^ --metadata-file metadata.yaml
 
-%.html: %.md
-	pandoc -s $(OPTIONS) $(HTMLOPTIONS) -o $@ $<
+cours.html: 01_rappel.md 02_integrales.md 03_optimisation.md 04_edo.md 05_fourier.md 06_probas_stats.md 07_remerciements.md 08_notes.md
+	pandoc -s $(OPTIONS) $(HTMLOPTIONS) -o $@ $^ --metadata-file metadata.yaml
 
 deploy: all
 	mkdir -p mti

metadata.yaml

@@ -16,7 +16,7 @@ documentclass: book
 papersize: A4
 cref: false
 urlcolor: blue
-header-includes:
+include-before:
 - |
   ```{=latex}
   \newcommand{\ux}{\bm{x}}