262 RELATION OF DECREMENTS TO 



the indices may be greater or less than either of 

 the others, in reference to particular modifying 

 planes. 



Decrements on the terminal edges. 



The planes produced by these decrements are all 

 comprehended under class /, although they may be 

 said to consist of three varieties. 



Jst. When the decrements proceed along the 



plane P. 

 2d. When the edge at which the planes / inter- 



sect each other at the base, is parallel to a 



diagonal of that base. 

 3d. When the decrements proceed along the plane 



M. 



The general symbol of the 1st, is B' p P B. 



2d, 'B'. 



Decrements upon the edge D of the base. 



P 



General symbol D. 

 p 

 If p zz 1, the symbol represents mod. m. 



p > 1, ....... class n. 



Decrements upon the edge F of the base. 



General symbol F. 

 p 



If p zz 1, the symbol represents mod. o. 

 p > 1, ....... class p. 



