Forms Authentication : Check logon status

I am coding up and email change process.
When the member comes back to the site after verifingt the new email address, I need to check if he/she is logged on ( ie cookie is active) to the site for redirection. And If he/she is not logged on maybe log them on then redirect..



So How do I do this logic?
If Member logged on (member found and logged on) = true
   1) redirect here to members page

else if membership is found = true but logged on = false  then

  1) Logon member
  2) redirect here to members page
else

1) redirect here to public page


NOTE: Interested in forms functions that do BOLD underlines logic 


Thanks



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