C = {companies}, e.g.: Microsoft, Apple

Ra= {Buy,Sell, Hold} ratings

I = {investors}, e.g.: JP Morgan Chase, John Doe

CR = {(c,r) | (c,r) C X Ra and company c's stock is assigned rating r}

IC = {(i , c) | (i ,c) I X C and investor i owns stocks of company c}

ICN = {(i,c,n) | (i,c,n) l x C x N and investor i holds n shares of company c}

Use a set builder notation and set operations to define a set S of companies whose shares are held by all investors

the answer should be some what like this

S = { c | c C and ({c} I) IC}