diff --git a/swad_agenda.c b/swad_agenda.c
index 7e1b6efb..c8a5f7ed 100644
--- a/swad_agenda.c
+++ b/swad_agenda.c
@@ -1080,8 +1080,7 @@ static void Agd_GetventDataByCod (struct Agd_Event *AgdEvent)
       /* Get whether the event is public or not (row[1])
          and whether it is hidden or not (row[2])  */
       AgdEvent->Public = (row[1][0] == 'Y');
-      AgdEvent->HiddenOrVisible = (row[2][0] == 'Y') ? HidVis_HIDDEN :
-	                                               HidVis_VISIBLE;
+      AgdEvent->HiddenOrVisible = HidVid_GetHiddenOrVisible (row[2][0]);
 
       /* Get start date (row[3]) and end date (row[4]) in UTC time */
       AgdEvent->TimeUTC[Dat_STR_TIME] = Dat_GetUNIXTimeFromStr (row[3]);
diff --git a/swad_assignment.c b/swad_assignment.c
index 22e149c6..f4887e3b 100644
--- a/swad_assignment.c
+++ b/swad_assignment.c
@@ -881,8 +881,7 @@ static void Asg_GetAssignmentDataFromRow (MYSQL_RES **mysql_res,
       Asg->AsgCod = Str_ConvertStrCodToLongCod (row[0]);
 
       /* Get whether the assignment is hidden or not (row[1]) */
-      Asg->HiddenOrVisible = (row[1][0] == 'Y') ? HidVis_HIDDEN :
-						  HidVis_VISIBLE;
+      Asg->HiddenOrVisible = HidVid_GetHiddenOrVisible (row[1][0]);
 
       /* Get author of the assignment (row[2]) */
       Asg->UsrCod = Str_ConvertStrCodToLongCod (row[2]);
diff --git a/swad_attendance.c b/swad_attendance.c
index a5b40089..80e29ed3 100644
--- a/swad_attendance.c
+++ b/swad_attendance.c
@@ -764,8 +764,7 @@ void Att_GetEventDataFromRow (MYSQL_ROW row,struct Att_Event *Event)
    Event->CrsCod = Str_ConvertStrCodToLongCod (row[1]);
 
    /***** Get whether the attendance event is hidden or not (row[2]) *****/
-   Event->HiddenOrVisible = (row[2][0] == 'Y') ? HidVis_HIDDEN :
-	                                         HidVis_VISIBLE;
+   Event->HiddenOrVisible = HidVid_GetHiddenOrVisible (row[2][0]);
 
    /***** Get author of the attendance event (row[3]) *****/
    Event->UsrCod = Str_ConvertStrCodToLongCod (row[3]);
diff --git a/swad_banner.c b/swad_banner.c
index ef418c85..bd79ba79 100644
--- a/swad_banner.c
+++ b/swad_banner.c
@@ -342,8 +342,7 @@ static void Ban_GetBannerDataFromRow (MYSQL_RES *mysql_res,
       Err_WrongBannerExit ();
 
    /***** Get if the banner is hidden (row[1]) *****/
-   Ban->HiddenOrVisible = (row[1][0] == 'Y') ? HidVis_HIDDEN :
-					       HidVis_VISIBLE;
+   Ban->HiddenOrVisible = HidVid_GetHiddenOrVisible (row[1][0]);
 
    /***** Get short name (row[2]), full name (row[3]),
           image (row[4]) and URL (row[5]) of the banner *****/
diff --git a/swad_browser.c b/swad_browser.c
index 62556f56..4bb61c05 100644
--- a/swad_browser.c
+++ b/swad_browser.c
@@ -4515,7 +4515,8 @@ static void Brw_PutIconToContractFolder (const char *FileBrowserId,const char *R
    switch (HiddenOrVisible)
      {
       case HidVis_HIDDEN:
-	 HTM_DIV_Begin ("id=\"contract_%s_%s\" style=\"display:none;\"",
+	 HTM_DIV_Begin ("id=\"contract_%s_%s\" class=\"NOT_SHOWN\"",
+	 // HTM_DIV_Begin ("id=\"contract_%s_%s\" style=\"display:none;\"",
 			FileBrowserId,RowId);
 	 break;
       case HidVis_VISIBLE:
@@ -7458,8 +7459,7 @@ HidVis_HiddenOrVisible_t Brw_CheckIfFileOrFolderIsSetAsHiddenInDB (Brw_FileType_
       row = mysql_fetch_row (mysql_res);
 
       /* File is hidden? (row[0]) */
-      HiddenOrVisible = (row[0][0] == 'Y') ? HidVis_HIDDEN :
-	                                     HidVis_VISIBLE;
+      HiddenOrVisible = HidVid_GetHiddenOrVisible (row[0][0]);
      }
    else
      {
diff --git a/swad_changelog.h b/swad_changelog.h
index 6de072a1..ad927017 100644
--- a/swad_changelog.h
+++ b/swad_changelog.h
@@ -628,11 +628,15 @@ TODO: Emilce Barrera Mesa: Quiero preguntarte si es posible que me habilites la
 TODO: Emilce Barrera Mesa: Podrías agregar por favor una opción que me permita exportar en excel, cvs o pdf el listado de estudiantes y la nota optenida en el examen. Eso me ayudaría mucho a la hora de pegarlas en mi planilla de excel.
 TODO: Emilce Barrera Mesa: Mis estudiantes presentan muchas dificultades a la hora de poner la foto porque la plataforma es muy exigente respecto al fondo de la imagen.
 
+TODO: Francisco Javier Fernández Baldomero: intento mandar un mensaje a un estudiante vacío sin nickname, que se debe haber creado hoy mismo otro usuario con DNI distinto y nickname
+Me sale este error, no sé si por no recordar yo la sintaxis apropiada para mandar a varios destinatarios. ¿No era así?
+"can npt create received message (duplicated entry '243218-2160773' for key 'UsrCod_MsgCod')
 */
-#define Log_PLATFORM_VERSION	"SWAD 23.0 (2023-09-11)"
+#define Log_PLATFORM_VERSION	"SWAD 23.0.1 (2023-09-11)"
 #define CSS_FILE		"swad22.120.4.css"
 #define JS_FILE			"swad22.49.js"
 /*
+	Version 23.0.1:	  Sep 11, 2023  Code refactoring related to hidden-visible. (337586 lines)
 	Version 23.0:	  Sep 11, 2023  Code refactoring related to hidden-visible. (337588 lines)
 	Version 22.120.17:Sep 10, 2023  Code refactoring related to hidden-visible in surveys. (337563 lines)
 	Version 22.120.16:Sep 10, 2023  Code refactoring in project visibility. (337575 lines)
diff --git a/swad_exam.c b/swad_exam.c
index 17fc02e7..65d281a1 100644
--- a/swad_exam.c
+++ b/swad_exam.c
@@ -896,8 +896,7 @@ void Exa_GetExamDataByCod (struct Exa_Exam *Exam)
       Exam->CrsCod = Str_ConvertStrCodToLongCod (row[1]);
 
       /* Get whether the exam is hidden (row[2]) */
-      Exam->HiddenOrVisible = (row[2][0] == 'Y') ? HidVis_HIDDEN :
-						   HidVis_VISIBLE;
+      Exam->HiddenOrVisible = HidVid_GetHiddenOrVisible (row[2][0]);
 
       /* Get author of the exam (row[3]) */
       Exam->UsrCod = Str_ConvertStrCodToLongCod (row[3]);
diff --git a/swad_exam_session.c b/swad_exam_session.c
index f39afc6c..2493889b 100644
--- a/swad_exam_session.c
+++ b/swad_exam_session.c
@@ -758,8 +758,7 @@ static void ExaSes_GetSessionDataFromRow (MYSQL_RES *mysql_res,
       Err_WrongExamExit ();
 
    /* Get whether the session is hidden (row[2]) */
-   Session->HiddenOrVisible = (row[2][0] == 'Y') ? HidVis_HIDDEN :
-						   HidVis_VISIBLE;
+   Session->HiddenOrVisible = HidVid_GetHiddenOrVisible (row[2][0]);
 
    /* Get session teacher (row[3]) */
    Session->UsrCod = Str_ConvertStrCodToLongCod (row[3]);
diff --git a/swad_game.c b/swad_game.c
index b4abc3cc..c29a8434 100644
--- a/swad_game.c
+++ b/swad_game.c
@@ -952,8 +952,7 @@ void Gam_GetGameDataByCod (struct Gam_Game *Game)
       Game->CrsCod = Str_ConvertStrCodToLongCod (row[1]);
 
       /* Get whether the game is hidden (row[2]) */
-      Game->HiddenOrVisible = (row[2][0] == 'Y') ? HidVis_HIDDEN :
-						   HidVis_VISIBLE;
+      Game->HiddenOrVisible = HidVid_GetHiddenOrVisible (row[2][0]);
 
       /* Get author of the game (row[3]) */
       Game->UsrCod = Str_ConvertStrCodToLongCod (row[3]);
diff --git a/swad_program.c b/swad_program.c
index c8d2bbcf..5f2ad6a9 100644
--- a/swad_program.c
+++ b/swad_program.c
@@ -1188,8 +1188,7 @@ void Prg_GetListItems (void)
          Prg_Gbl.List.Items[NumItem].Level  = Str_ConvertStrToUnsigned (row[2]);
 
 	 /* Get whether the program item is hidden or not (row[3]) */
-	 Prg_Gbl.List.Items[NumItem].HiddenOrVisible = (row[3][0] == 'Y') ? HidVis_HIDDEN :
-									    HidVis_VISIBLE;
+	 Prg_Gbl.List.Items[NumItem].HiddenOrVisible = HidVid_GetHiddenOrVisible (row[3][0]);
         }
      }
 
@@ -1257,8 +1256,7 @@ static void Prg_GetItemDataFromRow (MYSQL_RES **mysql_res,
       Item->Hierarchy.Level = Str_ConvertStrToUnsigned (row[2]);
 
       /* Get whether the program item is hidden or not (row[3]) */
-      Item->Hierarchy.HiddenOrVisible = (row[3][0] == 'Y') ? HidVis_HIDDEN :
-							     HidVis_VISIBLE;
+      Item->Hierarchy.HiddenOrVisible = HidVid_GetHiddenOrVisible (row[3][0]);
 
       /* Get author of the program item (row[4]) */
       Item->UsrCod = Str_ConvertStrCodToLongCod (row[4]);
diff --git a/swad_program_resource.c b/swad_program_resource.c
index ffd6fabe..ff250710 100644
--- a/swad_program_resource.c
+++ b/swad_program_resource.c
@@ -352,8 +352,7 @@ static void PrgRsc_GetResourceDataFromRow (MYSQL_RES *mysql_res,
    Item->Resource.Hierarchy.RscInd = Str_ConvertStrToUnsigned (row[2]);
 
    /***** Get whether the program item is hidden (row(3)) *****/
-   Item->Resource.Hierarchy.HiddenOrVisible = (row[3][0] == 'Y') ? HidVis_HIDDEN :
-								   HidVis_VISIBLE;
+   Item->Resource.Hierarchy.HiddenOrVisible = HidVid_GetHiddenOrVisible (row[3][0]);
 
    /***** Get link type and code (row[4], row[5]) *****/
    Item->Resource.Link.Type = Rsc_GetTypeFromString (row[4]);
diff --git a/swad_project.c b/swad_project.c
index 401d7c18..018af57a 100644
--- a/swad_project.c
+++ b/swad_project.c
@@ -3370,8 +3370,7 @@ void Prj_GetProjectDataByCod (struct Prj_Project *Prj)
 	    and whether the project is assigned or not (row[5]) */
 	 Prj->Locked   = (row[3][0] == 'Y') ? Prj_LOCKED :
 					      Prj_UNLOCKED;
-	 Prj->Hidden   = (row[4][0] == 'Y') ? HidVis_HIDDEN :
-					      HidVis_VISIBLE;
+	 Prj->Hidden   = HidVid_GetHiddenOrVisible (row[4][0]);
 	 Prj->Assigned = (row[5][0] == 'Y') ? Prj_ASSIGNED :
 					      Prj_NONASSIG;
 
diff --git a/swad_survey.c b/swad_survey.c
index dccb73fe..b702948e 100644
--- a/swad_survey.c
+++ b/swad_survey.c
@@ -1147,8 +1147,7 @@ void Svy_GetSurveyDataByCod (struct Svy_Survey *Svy)
       Svy->HieCod = Str_ConvertStrCodToLongCod (row[2]);
 
       /* Get whether the survey is hidden (row[3]) */
-      Svy->Status.HiddenOrVisible = (row[3][0] == 'Y') ? HidVis_HIDDEN :
-							 HidVis_VISIBLE;
+      Svy->Status.HiddenOrVisible = HidVid_GetHiddenOrVisible (row[3][0]);
 
       /* Get roles (row[4]) */
       if (sscanf (row[4],"%u",&Svy->Roles) != 1)
@@ -2120,15 +2119,11 @@ static void Svy_CreateGrps (long SvyCod)
 
 static void Svy_GetAndWriteNamesOfGrpsAssociatedToSvy (struct Svy_Survey *Svy)
   {
+   extern const char *HidVis_GroupClass[HidVis_NUM_HIDDEN_VISIBLE];
    extern const char *Txt_Group;
    extern const char *Txt_Groups;
    extern const char *Txt_and;
    extern const char *Txt_The_whole_course;
-   static const char *GroupClass[HidVis_NUM_HIDDEN_VISIBLE] =
-     {
-      [HidVis_HIDDEN ] = "ASG_GRP_LIGHT",
-      [HidVis_VISIBLE] = "ASG_GRP",
-     };
    MYSQL_RES *mysql_res;
    MYSQL_ROW row;
    unsigned NumGrps;
@@ -2139,7 +2134,8 @@ static void Svy_GetAndWriteNamesOfGrpsAssociatedToSvy (struct Svy_Survey *Svy)
 
    /***** Write heading *****/
    HTM_DIV_Begin ("class=\"%s_%s\"",
-                  GroupClass[Svy->Status.HiddenOrVisible],The_GetSuffix ());
+		  HidVis_GroupClass[Svy->Status.HiddenOrVisible],
+		  The_GetSuffix ());
       HTM_TxtColonNBSP (NumGrps == 1 ? Txt_Group  :
 				       Txt_Groups);