Подпись:   http://rlst.org.by/bulletin/bulletin061_5.htm                                                                            

Подпись:   http://lib.chernmmc.edusite.ru/p33aa1.html                                                                                                                                                                                                         

Подпись: http://www.acis.vis.ru/8/2/2_1/Ermakova.htm                                                                                                                                                                                    

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