Equation Icon   [ ] 2 2 l2 + 2 - 2 + - 2t 2 ds = dt - -- (r1 ) + (r1 ) + 2r1 r1 cos-- dx 4 [ l ] l2 + + - - + - - + 2t - 2 r1 r2 + r1 r 2 + (r1 r2 + r1 r2 )cos l dxdy 2[ ] - l- (r+ )2 + (r- )2 + 2r+ r-cos 2t dy2, (40) 4 2 2 2 2 l