got it! after talking with raph, who suggested using net_flow_max_flow() on a per-user basis, i coded this up, checking the node_in_degrees (accumulated number of certifications in to a user at and above a certain level) is greater than the number of certs required. entry from ChangeLog:

Sun May 14 02:37:15 PDT 2000 Luke Kenneth Casson Leighton
<lkcl@samba.org>

 	* got it!  requires:
	- a call to net_flow_max_flow on a per-user
	basis, with the user as the seed.

 	- return of node_in_degrees * node_flow
	because node_in_degrees  tells you how many 
	paths there are into the seed [the user]

 	consequence: if each user has flow in from
	other users at a level
	equal to or above their own (node_flow[level] == 1),
	and the number of paths 
	(node_in_degrees[level] >= min_certs_reqd[level)
	to them is greater or equal to the number required
	to be certified at that level

 	*AND*

 	overall, they are certified in the "general"
	trust metric at that level

 	*THEN*

 	the certification is accepted.