// Constreuctor
 public Lending(DateTime ld,
                User u,
                SourceOfInformation m,
                DateTime rd)
 {
     // Initializing the attibutes
     lendDate            = ld;
     material            = m;
     luser               = u;
     returnDate          = rd;
     returnedDate        = rd;
     returnedInGoodState = false;
 }
 // To return a lending
 public Lending ReturnASource(User u, SourceOfInformation s, DateTime d)
 {
     // TO DO
     throw new NotImplementedException();
 }
 // To lend a source
 public bool LendASource(User u, SourceOfInformation s, DateTime d)
 {
     //  TO DO
     return(false);
 }
 // To add a new source
 public void AddNewSourceOfInformation(SourceOfInformation soi)
 {
     //  TO DO
     throw new NotImplementedException();
 }