I've been reading about Super Resolution Image reconstruction (Reconstruction of high resolution image from multiple low resolution aliased images contain sub pixel shifts), and i want to know why SR is possible? this [document](http://www.mediafire.com/view/epo73vcq5xzhxw8/Aggelos_Katsaggelos-Super_Resolution_of_Images_and_Video_%28Synthesis_Lectures_on_Image,_Video,_and_Multimedia_Processing%29-Morgan.pdfg) explains why SR is possible, but i didn't understand completely!

please can you explain more clearly.