Kepler & K2 provide long-baseline, high-precision photometry for exoplanet and astrophysics research.
The basic and most common additional rule for Doubles play is that where a Double exists at the end of any train, the Double must then be 'satisfied' (laid against) in the next turn, even if the Double is on another player's train that is not marked.
Fartlek training or 'speed play' training involves varying your speed and the type of terrain over which you run, walk, cycle or ski. It improves aerobic and anaerobic fitness. Interval training involves alternating between periods of hard exercise and rest. It improves speed and muscular endurance.