So, suppose you purify protein, and that protein consists of seven amino acids. Now, your goal is to basically find what the exact sequence of amino acids is in that given protein. And what you do is you expose the protein to two different proteolytic agents, thereby producing two sets of different fragments. So in experiment number one, you take your seven amino polypeptide, you expose it to trypsin. And what trypsin does is it essentially cleaves at the carboxyl end of lysine and arginine. And what you obtain is these three fragments.