None of the overloads of 
insert_after shall affect the validity of iterators and
references, and 
erase_after shall invalidate only iterators and references to
the erased elements
.If an exception is thrown during 
insert_after there shall
be no effect
.Inserting 
n elements into a 
forward_list is linear in
n, and the number of calls to the copy or move constructor of 
T is
exactly equal to 
n.Erasing 
n elements from a 
forward_list is
linear in 
n and the number of calls to the destructor of type 
T is
exactly equal to 
n.