Encoding_instantiate keeps the type of the green part complexe.
Encoding_simple2 (bad name) replaces the complexe types by constants.

One day we can add a better comprehesion of (int,int) array for instance
 inside encoding_simple2 or inside the printers.

bridge      + decorate : kept
instantiate + decorate : kept goal

= replaced by ls_equal in core/pretty (was discovered thanks to a Invalid_argument(equal: functional value)