Remove the specified members from the set stored at `key`. Specified members
that are not a member of this set are ignored. If `key` does not exist, it is
treated as an empty set and this command returns `0`.

An error is returned when the value stored at `key` is not a set.

@return

@integer-reply: the number of members that were removed from the set, not
including non existing members.

@history

- `>= 2.4`: Accepts multiple `member` arguments. Redis versions older than 2.4
  can only remove a set member per call.

@examples

```cli
SADD myset "one"
SADD myset "two"
SADD myset "three"
SREM myset "one"
SREM myset "four"
SMEMBERS myset
```