Simple question, but it is causing me a lot of headache...

Is there a difference between SE and Sigma(E)?

Similarly between R and r?

The book itslef seems to use both notations, which has made me search long and hard for a difference...

[NEAS: Statisticians use these abbreviations slightly different ways, but the final exam problems treat them the same. For instance, the standard error of the regression refers to the response variable, whereas the standard deviation of the error term refers to the residual; lower case r is the correlation of any two random variables, whereas upper case R is the square root of the multiple correlation in a regression analysis. Don't worry about these differences; if you see the overlap, you understand the material.]