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