LaTeX.org

I'm using fancyhdr package. I added in the preamble the following commands:
\fancyhead[LE]{\sffamily\nouppercase{\leftmark}}
\fancyhead[RO]{\sffamily\nouppercase{\leftmark}}
That is, the section name should appear on the left side header on even pages (LE), and on the right side header on odd ...