let rec append = function l ->
  match l with
    | [] -> function l -> l
    | h::t -> function l -> h::(append t l) ;;

• si l₁ est vide, appendl₁(appendl₂l₃) = appendl₂l₃ et append(appendl₁l₂)l₃ = appendl₂l₃
  
  
• sinon l₁ = h₁::l₁' et

  appendl1(appendl2l3)	=	h1::(appendl1'(appendl2l3))
  append(appendl1l2)l3	=	append(h1::(appendl1'l2))l3
  	=	h1::(append(appendl1'l2)l3)