Cradling the lower leg and rocking laterally is often taught in hatha yoga courses. The half lotus and full lotus postures came from the yogis and Buddhist monks from India. The Burmese meditation posture may be easier for many in that both feet are on the floor while sitting. See http://www.abc-of-yoga.com/meditation/poses.asp Another easy posture is the kneeling position common in Japan http://www.buddhamind.info/leftside/lifestyl/medi/posture.htm A meditation stool can make this pose much easier to hold for long periods.

The hurdler's stretch is also another good practice exercise. If you go beyond the hype, the body flow system by Coach Sonnon has some excellent flexibility exercises for the lower body to develop the suppleness to achieve full lotus much more quickly.
http://www.amerross.com/kinetic.html

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