let ajouter x y  = y^x;;
let ajouter_a_tous x y = List.map (ajouter y) x;;
let x = ["";"";""];;
let x = ref x;;
let add x y = x:=ajouter_a_tous !x y ;;
x;;
add x "Salut";;
x;;
add x " toi";;
x;;