When buying 20 or more tickets for a performance, you will receive an additional free ticket. Use the special offer. 

When buying at least ...

... 20 tickets pro for a performance with a *, you will receive
10 additional Tickets of the predominant category.

... 30 tickets pro for a performance with a *, you will receive
15 additional Tickets of the predominant category.

... 10 season tickets you will receive,
2 additional Season Tickets of the predominant category.

The offer does not apply to day tickets !