proofgeneral: 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/proofgeneral - from package: proofgeneral

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

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