-= removes certain things from a set, e.g. Field -= Value1 will return a set of all non-Value1 (and non-null) values from Field.
E() means values excluded by a specific subset. You should look up the documentation for this for examples, but one example is:
sum( {$<Customer = E({1<Product={‘Shoe’}>})>} Sales )
returns the sales for current selection, but only those customers that never bought the product ‘Shoe’. The element function E( ) here returns the list of excluded customers; those that are excluded by the selection ‘Shoe’ in the field Product.
