OK, Without ASL below are the base permutations. From that let's eliminate some obvious "I doubt anyone would do this"

Based on Russells comment that most bridges involve DMR
DMR <-> D-Stsr
DMR <-> YSF
DMR <-> NXDN
DMR <-> P25

D-Star <-> YSF
D-Star <-> NXDN
D-Star <-> P25 (I doubt anyone would do this)

YSF <-> NXDN
YSF <-> P25

NXDN <-> P25

BTW, this kinda ignores YSFn vs YSFw

Anyone else care to eliminate a bridge? I'm leaning to create the first four Subgroups and see what happens.

Steve