reword security section

[job]

reword section on IPv4 vs IPv6 incongruence, remove expectations, hint at future work

[job]

Ping?

[mitradir]

I suggest next wording:

      The U-SPAS contain the union of Providers for a CAS for both IPv4 and IPv6 unicast connectivity.

      This design choice consequently means that if a customer-provider relationship exists only in one address family, and it doesn't exist in the other one address family, AS_PATH verification outcomes in the latter AFI will be as permissive as verification outcomes in the former AFI.

      That is believed to be a reasonable compromise as both the ASPA registration and verification processes are simplified, and no false positive outcomes are yielded (e.g. inadvertent Invalid evaluation).

The later part seems to be irrelevant to the security consideration section, since it partially describes Complex relation case, partially speaks about later developments that may happen or may not.

[job]

ok, amended