Where does the notation $\mbox{Soc}(M)$ (the sum of all simple submodules of a module $M$) first appear? 



Origin of the Socle of a module
This [book](http://rads.stackoverflow.com/amzn/click/082184900X) by J. Lambek says on page 168 that the notion of socle (for modules) is due to Dieudonne. In [this paper](https://eudml.org/doc/86762), the word "socle" is used by Dieudonne, and he explains that he follows M.R. Remak, who first introduced the notion of socle for finite groups, as a subgroup generated by all minimal normal subgroups. However, I cannot find yet where the notation "Soc" appears first (in the context of modules). 


Hope this bit of information helps. Cheers! 


