// TODO: Extend IDocument instead, rename to WhereDocumentType
 public static IEnumerable <IDocument> GetDocumentsOfType(this IEduProgram eduProgram, SystemDocumentType documentType)
 {
     return(eduProgram.Documents.Where(d => d.GetSystemDocumentType() == documentType));
 }
 public static IEnumerable<IDocument> GetDocumentsOfType (this IEduProgram eduProgram, SystemDocumentType documentType)
 {
     return eduProgram.Documents.Where (d => d.GetSystemDocumentType () == documentType);
 }