t = +(*(a(#,#),b(#,#)),/(c(#,#),d(#,#)))
size(t) = 7
computation of size(t) :
'+'
>       '*'
>       >       'a'
>       >       >       #
>       >       >       size = 0
>       >       >       #
>       >       >       size = 0
>       >       size = 1
>       >       'b'
>       >       >       #
>       >       >       size = 0
>       >       >       #
>       >       >       size = 0
>       >       size = 1
>       size = 3
>       '/'
>       >       'c'
>       >       >       #
>       >       >       size = 0
>       >       >       #
>       >       >       size = 0
>       >       size = 1
>       >       'd'
>       >       >       #
>       >       >       size = 0
>       >       >       #
>       >       >       size = 0
>       >       size = 1
>       size = 3
size = 7