The primary link is almost always to the canonical version which is usually the pay walled one(even if it's not the most in depth version the author wrote). Di

The primary link is almost always to the canonical version which is usually the pay walled one(even if it's not the most in depth version the author wrote). Did you check for the links on the right hand side? Those are the pdf's that google found. Of a pseudo random set I clicked on, all had links.