mem mgt

2.18: adda/mem mgt:
. one way to handle dangling ptr's is
have pointer be to a ptr var that
holds the ptr to target value (ie, sharers are handles)?
if there's a chance that var will be dealloc'd
then must have a global place for sharables .


2.21:

adda/mem'mgt/cyclic structures:
. one way to handle cyclic graphs
is have each node carry an [has been copied].bit
and copy recursively whenever that bit's not set .