Update textbook.es.md

00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/04.reference-frames-coordinate-systems/textbook.es.md

@@ -9,11 +9,14 @@ $`\def\Ltau{\Large{\tau}\normalsize}`$
 $`\def\Sopen{\mathscr{S}_{\smile}}`$
 $`\def\Sclosed{\mathscr{S}_{\displaystyle\tiny\bigcirc}}`$
 $`\def\Ssclosed{\mathscr{S}_{\scriptsize\bigcirc}}`$
-$`\def\\Sclosed{\mathscr{S}_{\smile}}`$
+$`\def\Sclosed{\mathscr{S}_{\smile}}`$
 $`\def\PSclosed{\mathscr{S}_{\displaystyle\tiny\bigcirc}}`$
 $`\newcommand{\Sopen}{\mathscr{S}_{\smile}}`$
 $`\newcommand{\Ssclosed}{\mathscr{S}_{\displaystyle\tiny\bigcirc}}`$
-$`\newcommand{Sclosed}{\mathscr{S}_{\displaystyle\tiny\bigcirc}}`$
+$`\newcommand{\Sclosed}{\mathscr{S}_{\displaystyle\tiny\bigcirc}}`$
+
+* $`\Sopen`$
+* $`\Sclosed`$
 
 ### Elementos del curso : las sistemas de coordenadas / Eléments de cours : les systèmes
 de coordonnées / Course elements : the coordinate systems