Return the difference between the Set stored at key1 and all the Sets key2, ..., keyN
<p>
<b>Example:</b>
<pre>
key1 = [x, a, b, c]
key2 = c
key3 = [a, d]
SDIFF key1,key2,key3 => [x, b]
</pre>
Non existing keys are considered like empty sets.
<p>
<b>Time complexity:</b>
<p>
O(N) with N being the total number of elements of all the sets
@param keys
@return Return the members of a set resulting from the difference between the first set
provided and all the successive sets.
Return the difference between the Set stored at key1 and all the Sets key2, ..., keyN <p> <b>Example:</b>
<pre> key1 = [x, a, b, c] key2 = c key3 = [a, d] SDIFF key1,key2,key3 => [x, b] </pre>
Non existing keys are considered like empty sets. <p> <b>Time complexity:</b> <p> O(N) with N being the total number of elements of all the sets @param keys @return Return the members of a set resulting from the difference between the first set provided and all the successive sets.