How call javascript onClick event on checkbox prompt

[SimoCogn]

Hi all,
i need to implement a check on the values of two multivalue checkbox prompts in a report:
i'll call it prompt A and prompt B.

Initally prompt A is selected by default and prompt B is all unselected. The two prompt must be mutually exclusive, so when i select (click) a checkbox of prompt A , i must unselect all values of prompt B, and if i select a checkbox of prompt B , i must unselect all values of prompt A.

I have thinked to create a javascript that unselect all the values of prompt A or B, but my problem is that i don't know how to start this script onClick event on the two checkbox prompt. I use cognos version 10.2


Thanks for any suggestions

regards
Simon