Is there a shortcut for 'SELECT * FROM table' in relational algebra?
Yes.

In relational algebra the relation

Book

corresponds to

select * from Book


If you want to restrict to some rows you apply a selection &sigma;:

&sigma;ISBN=43221(Book)

In SQL this is a where-clause like

select * from Book where ISBN=43221


If you want to reduce the columns you need a projection &pi;:

&pi;ISBN, title, type(&sigma;ISBN=43221(Book))

In SQL this is a select-list different from *: 

select ISBN, title from Book where ISBN=43221