isofilter: 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/isofilter - from package: prover9

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

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