In a sectional matchpoint event you show up, planning to kibitz two strong players you know. Unfortunately, there are an odd number of pairs in the section and the director notices you and another kibitzer hanginf around, so shoves the two of you at gunpoint into the two empty seats. During the 45 seconds that you have to discuss system methods you agree on "fairly basic 2/1" and a few other things (UDCA, natural over opponents' strong NT, ....). Favorable vulnerability. Partner passes, RHO opens a 15-17 NT, you bid a "natural" 2C, and the auction proceeds P-(1N)-2C-(P)-2D-(P)-P-(2H)-X..... OK, what is that double?