APERFORMANCE of Solid Longing is more than a collaboration between choreographers. It's a family reunion. Colleen Mulvihill and Eponine Cuervo Moll met 10 years ago in San Francisco and became good friends. They live in the same artist community in Oakland, California and share many interests. It was Moll who introduced Mulvihill to martial arts. Another common denominator is their significant others. J. A. Deane and Andrew Voigt are not only friends, but musicians and composers. When their girlfriends decided to produce Solid Longing the men agreed to write the music then join them in Hongkong to perform it. Besides dance and music, the artists use slides, film, poetry and Chinese martial arts in the work. When the production, sponsored by the City Contemporary Dance Company, opens tomorrow evening at the Shouson Theatre, the rendezvous will have come full circle. The month-long working holiday for Mulvihill and Moll has been arduous yet satisfying. They made time for morning sessions with Moll's martial arts teacher and the enthusiasm generated by the CCDC dancers has been infectious. It was Moll's idea to pursue the conflicts between man and woman as a theme. Of the nine sketches, Mulvihill wrote three, Moll, four and they pooled on one. ''She is very dynamic, very physical,'' said Moll, of the American's choreographic style. Hardly a surprise. At the age of 15, Colleen Mulvihill was the youngest gymnast on the American team to compete in the 1968 Mexico City Olympics. ''I don't remembermuch of it. I think I was in shock.'' Her father, who was also her coach, always stressed the expressive aspect of gymnastics. Following the Olympics, she retired and entered the world of modern dance. Moll uses words like choreo-visualisation and transference in talking about her ideas. A psychologist by training, the Colombian-born artist evolved into a painter-musician-writer. ''As a child I was always staging something. Then, as a therapist, I wasacting things out with clients. ''I finally realised that what I was really doing [with clients] was theatre. So I switched from psychology and got into this.'' In 1982, she established her own company in San Francisco. Following athletics, Mulvihill studied modern dance with a variety of teachers, including Merce Cunningham. ''I knew there was something else in the movement field. In modern dance I found the possibilities.'' Her penchant for architecture shines through in her set designs. ''I go beyond the wall and floor,'' she said, referring to the specially-built steps, ramps and bars. In terms of physical stature, she still maintains the taut body of a gymnast, the ram-rod straight posture and agility. In coaching three young male dancers during a rehearsal recently, she executed the back-twisting moves first. ''Years ago I suffered a severe back injury,'' Mulvihill said. ''The doctor said I would never be able to dance well again. I proved him wrong.'' Of the role dance plays in her life: ''Dance is my passion. These dances I choreograph are my children. If I could, I'd be out there performing them.''