coqtop: 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/coqtop - from package: coq

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

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