yacas: 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:

/var/lib/wims/public_html/bin/yacas - from package: wims
/usr/bin/yacas - from package: yacas

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

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