isofilter2: 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/isofilter2 - from package: prover9

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

Error in other languages:
isofilter2: bevel nie gevind nie
isofilter2: comandă negăsită
isofilter2: comando não encontrado
isofilter2: commande introuvable
isofilter2: command not found
isofilter2: käsku ei ole
isofilter2: không tìm thấy lệnh
isofilter2: komanda nerasta
isofilter2: Kommando nicht gefunden.
isofilter2: kommandot finns inte
isofilter2: komut yok
isofilter2: nie znaleziono polecenia
isofilter2: níor aimsíodh an t-ordú
isofilter2: no se encontró la orden
isofilter2: no s'ha trobat l'ordre
isofilter2: opdracht niet gevonden
isofilter2: parancs nem található
isofilter2: perintah tidak ditemukan
isofilter2: príkaz nenájdený
isofilter2: příkaz nenalezen
isofilter2: команда не найдена
isofilter2: командата не е открита
isofilter2: 命令找不到
isofilter2: コマンドが見つかりません