Return true if member is a member of the set stored at key, otherwise false is returned.
<p>
Time complexity O(1)
@param key
@param member
@return bool reply, specifically: true if the element is a member of the set false if the element
is not a member of the set OR if the key does not exist
Return true if member is a member of the set stored at key, otherwise false is returned. <p> Time complexity O(1) @param key @param member @return bool reply, specifically: true if the element is a member of the set false if the element is not a member of the set OR if the key does not exist