///Returns a list of values from `$lists` minus duplicates.
///@ignore Documentation: http://sassylists.com/documentation.html#sl-union
///@requires sl-flatten
///@requires sl-remove-duplicates
///@param {ArgList} $lists - lists to unify
///@example
///		sl-union(a b c, b e d, a c b)
/// 	//a b c e d
///
///@return {List}
 
 
@function sl-union($lists...) {
  @if sl-missing-dependencies(sl-flatten, sl-remove-duplicates) == true { @return null; }

  $result: sl-remove-duplicates(sl-flatten($lists));
  
  @return $result;
}

///@requires sl-union
///@alias sl-union
@function sl-merge($lists...) {
  @return sl-union($lists...);
}