370 PROCEEDINGS OF THE AMERICAN ACADEMY. 



such expressions, the equations connecting them are not changed by 

 assuming JJ scalar. This amounts to making all progressive products 

 oi p letters scalar. 



The regressive product represents the space common to two spaces 

 or vanishes when they are contained in a space of order less than j^- 

 This product represents symbolically the second fundamental linear 

 process, and by its vanishing the second type of relation. 



