I first worked with Giancarlo when I visited him for the first time in Milan. I invited him to the Oberwolfach meeting on discrepancy in 2004, and visited him again in Milan in 2004. We have collaborated ever since we first started discussing mathematics. His very solid background on harmonic analysis has given fresh insight into quite a few problems on discrepancy theory through the study of the decay of Fourier transforms.
Giancarlo is a very hard-working and enthusiastic colleague, and he was the main force behind the 2007 discrepancy theory meeting held at the Villa Cipressi in Varenna in Italy. Here is a photo of us there, and it looks like we have just got a new idea!