tptp2dfg: 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/tptp2dfg - from package: spass

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

Error in other languages:
tptp2dfg: bevel nie gevind nie
tptp2dfg: comandă negăsită
tptp2dfg: comando não encontrado
tptp2dfg: commande introuvable
tptp2dfg: command not found
tptp2dfg: käsku ei ole
tptp2dfg: không tìm thấy lệnh
tptp2dfg: komanda nerasta
tptp2dfg: Kommando nicht gefunden.
tptp2dfg: kommandot finns inte
tptp2dfg: komut yok
tptp2dfg: nie znaleziono polecenia
tptp2dfg: níor aimsíodh an t-ordú
tptp2dfg: no se encontró la orden
tptp2dfg: no s'ha trobat l'ordre
tptp2dfg: opdracht niet gevonden
tptp2dfg: parancs nem található
tptp2dfg: perintah tidak ditemukan
tptp2dfg: príkaz nenájdený
tptp2dfg: příkaz nenalezen
tptp2dfg: команда не найдена
tptp2dfg: командата не е открита
tptp2dfg: 命令找不到
tptp2dfg: コマンドが見つかりません