I became a postdoc and start to work on the ALFALFA+SDSS project. Jessica Rosenberg is building up a cross-correlated catalog from blind HI survey ALFALFA and SDSS. Main goal of this project is to study a role of gas in galactic star formation and galaxy evolution, using a large number of HI and optical sample. Today Jessica gave a talk and showed some of preliminary results from the ALFALFA+SDSS. Although it was interesting to see that the gas-to-star ratio for galaxy pair is less than that for the entire ALFALFA+SDSS sample on average, a careful investigation of the sample selection function should be done for a reliable inference.