In reply to rkg_:
By now you have a good understanding of the concepts to address your requirements.
On the intersect sequence, define that length instead of 1 to 8 to something like
// that intersect event(isct0) should only active after the first posedge of inc or dec.
( (inc[->1] or dec[->1]]) ##1 1'b1[*1:8])
Again, by now you should understand this solution and the approach concepts.
The detailed implementation of the assertion is up to you.
Ben systemverilog.us