mathmlviewer: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/mathmlviewer - from package: libgtkmathview-bin

You may install the required package with command apt-get install {package}

Error in other languages:
mathmlviewer: bevel nie gevind nie
mathmlviewer: comandă negăsită
mathmlviewer: comando não encontrado
mathmlviewer: commande introuvable
mathmlviewer: command not found
mathmlviewer: käsku ei ole
mathmlviewer: không tìm thấy lệnh
mathmlviewer: komanda nerasta
mathmlviewer: Kommando nicht gefunden.
mathmlviewer: kommandot finns inte
mathmlviewer: komut yok
mathmlviewer: nie znaleziono polecenia
mathmlviewer: níor aimsíodh an t-ordú
mathmlviewer: no se encontró la orden
mathmlviewer: no s'ha trobat l'ordre
mathmlviewer: opdracht niet gevonden
mathmlviewer: parancs nem található
mathmlviewer: perintah tidak ditemukan
mathmlviewer: príkaz nenájdený
mathmlviewer: příkaz nenalezen
mathmlviewer: команда не найдена
mathmlviewer: командата не е открита
mathmlviewer: 命令找不到
mathmlviewer: コマンドが見つかりません