| Box.H (_,bl)::tl -> aux_h current_s (bl@tl)
| Box.V (_,[])::tl -> aux_h current_s tl
| Box.V (_,[b])::tl -> aux_h current_s (b::tl)
| Box.V (_,b::bl')::tl ->
aux_h current_s [b] ;
aux_h (String.make (String.length current_s) ' ') (Box.V([],bl')::tl)
| Box.H (_,bl)::tl -> aux_h current_s (bl@tl)
| Box.V (_,[])::tl -> aux_h current_s tl
| Box.V (_,[b])::tl -> aux_h current_s (b::tl)
| Box.V (_,b::bl')::tl ->
aux_h current_s [b] ;
aux_h (String.make (String.length current_s) ' ') (Box.V([],bl')::tl)