Try the homework assignment! There are two problems where you will use de novo sequencing to elucidate the sequence of the peptide and find the corresponding protein. There are 3 problems where you use the "rules of fragmentation" to figure out if a sequence assignment seems valid or if there are any issues with the assignment that might need to be resolved if it is to be used. The solutions are also available. Try to do the homework first before you use the solutions!