This is a book reference (1). Okuda and Okuda remarked this previously (1).

This is a journal article reference (2). Wilcox remarked this previously (2).

This is a newspaper article reference (3). Di Rado remarked this previously (3).

This is a newspaper article reference without an author (4). remarked this previously (4).

This is a magazine article reference (5). Di Rado remarked this previously (5).

This is a book chapter reference (6). James remarked this previously (6).

This is a web page reference (7). Lynch remarked this previously (7).