Spiegel , Eugene <br/><br/>
Incidence algebras. 
Eugene Spiegel and Christopher J. O' Donnell. 
 - New York:  Marce Decker,  1997. 
 - ix, 335p. 
<br/><br/><label>Subjects--Index Terms: </label>Incidence algebras. 
<br/><br/><label>Universal Decimal Class. No.: </label>512  / SPI