How to show, linked, the backrelationships of a TTW dexterity item in Plone 5.1?

[spanish]

Hello,

I have two TTW Dexterity content types (Room and Book).

I can, using RelationList, select books in a room and display the selected books on the room page.

How could I display (linked) the rooms where I selected a book on the page of that book?

I have Plone 5.1.6 and collective.relationhelpers 1.4.

If I add tal:define="inspect_backrelation python: view.inspect_backrelation;" to the book view template (inside a div or metal:content-core), I get this error: AttributeError: 'Plone' object has no attribute 'inspect_backrelation'.

@@inspect-relations + Show backrelations works fine (displays all backrelations fine).

I would sincerely appreciate your help.

Thanks!

Manuel