equation icon  ( ) ( ) F ab =_ q- 1- hab- 1gabhc [] 4 2 c q [ + -- \~/ c \~/ ahbc + \~/ c\ ~/ bhac- []hab - \~/ a\ ~/ bhcc- gab \~/ c\ ~/ dhcd + gab[]hcc 2 ( a b b a ab ab d ab d) c ab c d] + \~/ hc + \~/ hc - \~/ ch - 2g \~/ hcd + g \~/ ch d \~/ - g hcd \~/ \~/ . (33)