TOPIC: Ability to check if someone is in an event and if so, they can not register for another event

09.) Ability to check if someone is an event and if so, they can not
register for another event

ie: We have AD&D tournaments that run at different times. One might be
from 0800~1300 in the morning and another at 1300~1800 in the afternoon.
You can only be in ONE tourney no matter how may times it runs. So I need
a way to check to see if you are in another event of the same type
(group?) and then NOT allow you to be in this event. Since some events can
be in multiple "groups" ie: Thursday Games might be one group, and then
AD&D Tourney might be the other group.. .I'd need to be able to check an
either/or and/or either/both.... kinda of like I need the either option on
the other request I have in here some where.