local blanc = Color.new(255, 255, 255)

local mur = Image.createEmpty(20, 50)
mur:clear(blanc)

function MoveMur(statut, ymur)
    if ymur > 50 then
        statut = 0
    elseif ymur < 2
        then statut = 1
    end
    if statut == 1 then
        ymur = ymur + 1
    elseif statut == 0 then
        ymur = ymur -1
    end
    screen:blit(200, 0, mur, 0, 0, 20, ymur)
end

while true do
    screen:clear()

    MoveMur(1, 1)

    screen.waitVblankStart()
    screen.flip()
end