prover9: 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/prover9 - from package: prover9

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

Error in other languages:
prover9: bevel nie gevind nie
prover9: comandă negăsită
prover9: comando não encontrado
prover9: commande introuvable
prover9: command not found
prover9: käsku ei ole
prover9: không tìm thấy lệnh
prover9: komanda nerasta
prover9: Kommando nicht gefunden.
prover9: kommandot finns inte
prover9: komut yok
prover9: nie znaleziono polecenia
prover9: níor aimsíodh an t-ordú
prover9: no se encontró la orden
prover9: no s'ha trobat l'ordre
prover9: opdracht niet gevonden
prover9: parancs nem található
prover9: perintah tidak ditemukan
prover9: príkaz nenájdený
prover9: příkaz nenalezen
prover9: команда не найдена
prover9: командата не е открита
prover9: 命令找不到
prover9: コマンドが見つかりません