Hello Jean Michel,
Thank you for your answer and sorry for the delay in answering but we have been making a lot of tries. Now it works perfectly , we are using M2.6 and Adaptive mode (multi-part questions) 3.3.
With other combinations we had a blank page or this message
Fatal error: Call to undefined method qbehaviour_adaptivemultipart::adjust_display_options_for_part() in /home/a002573/public_html/0prova/moodle25/question/type/formulas/renderer.php on line 127
On the other hand I was confused as I was waiting for the formulas-adaptative with 2-parts, to show two submit-buttons, one for each subquestion (part). Now I see that only with one button it works OK.
Congratulations for your good work
Bernat