Proper syntax for Computed Column Specification

 Hi,
I have two date fields in my table (date1, date2).  I want a 3rd field to output a string based on these dates such that:
if date1<now then..."some string"
elseif date1>=now and date2<now then..."some string"
else..."some string"
Can someone point to some kind of syntax tutorial for this.
 Thx

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