Given sets X1,...,Xn the projection from the product X1 * ... *Xn is the function pri = prxi : X1 * ... *Xn → Xi , pri(t1, ..., ti, ...,tn) := ti Im having a hard time figuring out what exactly is going on here. Some coordinate from all sets X1 to Xn are getting multiplied together? The above bit is an introductory example/case of "the projection function". Any help will do. Thanks.