Thanks, Bill, for the answer. Of course I don't feel disparaged. I feel fortunate to have the opportunity to learn thanks to people like you, here and in another places.
And in the process I asume I will make lot of mistakes not only with Memento or javascript but also in the forums(which are also something relatively new for me).
With a new aproach to the problem I have arrive to a very close performace of what I was looking for. I will explain it in case is usefull for anyone.
I recall the matter:
I have a single-choice list field called "ESTADO:" with two items:("PENDIENTE" and "RESUELTO"). Item "PENDIENTE" is set as default.
I want that once I select "RESUELTO" item the "PENDIENTE" item does not show anymore to avoid the possibility to select it.
Finally, and thanks to Bill's help, I solved as follow:
I created a new page called "CÁLCULOS". In this page I created a boolean field called "valor del campo ESTADO: resuelto"(yes, is more a description than a name...) with format: On label: true. Off label: false. And set "false" as default. This field has no visual utility, so I set up a dependency in this field(dependent) to be always invisible, using as master field any other field of the library with choices.
Return to the MAIN page, I set up a dependency in the field "ESTADO:"(dependent) using field "valor del campo ESTADO: resuelto" of the "CÁLCULOS" page as master.
The depencency is a content dependency and is set up as follow: for the master field "valor del campo ESTADO: resuelto" value "true", the item "PENDIENTE" is no more available for selection. For the master field "valor del campo ESTADO: resuelto" value "false", both "PENDIENTE" and "RESUELTO" items are available for selection.
Then I create two triggers in this library containing the same script for different events:
one for event: updating an entry, phase: opening an entry edit card. No need of security permissions.
other for event: opening an etry view card, phase: before window display. No need of security permissions.
The script is:
var e = entry();
if (e.field("ESTADO:") == "RESUELTO")
e.set("valor del campo ESTADO: resuelto", true);
That's it.
There is only one problem. I set up the single-choice list field "ESTADO" to be editable in the entry list view. If I change the value of the "ESTADO" field in the entry list view tapping on its icon from "PENDIENTE" item to "RESUELTO" item and I tap againg the icon to it keeps showing the two items. I need to enter to entry view card or entry edit card to make the trigger run.
If anyone knows other way to do this or a way to improve this way I will be very grateful to know.
Sorry for so long post.