\ [:\ ddot {\ text {o}} - \ text {s}(=\ text {f})_ {2}(\ text {=o})_ {2} \ rightleftharpoons :\ ddot {\ text {o}} =\ text {s}(=\ text {f})_ {2}(\ text {=o})\ text {o}^ - \]
\ [:\ ddot {\ text {o}} - \ text {s}(=\ text {f})_ {2}(\ text {=o})_ {2} \ rightleftharpoons :\ ddot {\ text {o}} =\ text {s}(=\ text {f})_ {2}(\ text {=o})\ text {o}^ - \]