1. Series check: all three agree to order (v/c)^2
   special relativity                   F = 0.99498743710662   (1 - x/2 = 0.995)
   Aspden 1980 (2 - gamma)              F = 0.994962184740788   (1 - x/2 = 0.995)
   Aspden 1996 ((2 - beta^2) beta^3)    F = 0.994887938362909   (1 - x/2 = 0.995)
   exact: Aspden 1996 F/beta = 1 - (v/c)^4;  Aspden 1980 F/beta = 1 - (v/c)^4/4 + ...

2. Fast-ion Ives-Stilwell tests: eps = nu_a nu_p / nu0^2 - 1
   Heidelberg TSR, Li+ (Saathoff 2003; Reinhardt 2007)  (v = 0.064 c), measured 0.0 +/- 3.4e-10
      special relativity                   predicts eps =          0.0  -> 0.0 sigma
      Aspden 1980 (2 - gamma)              predicts eps =     -8.44e-6  -> 2.45e+4 sigma
      Aspden 1996 ((2 - beta^2) beta^3)    predicts eps =    -3.355e-5  -> 9.75e+4 sigma
   GSI ESR, Li+ (Botermann et al. 2014)  (v = 0.338 c), measured 1.5e-9 +/- 2.3e-9
      special relativity                   predicts eps =          0.0  -> 0.652 sigma
      Aspden 1980 (2 - gamma)              predicts eps =    -0.007806  -> 3.39e+6 sigma
      Aspden 1996 ((2 - beta^2) beta^3)    predicts eps =     -0.02593  -> 1.13e+7 sigma

3. In 1996 terms: the 1990s Ives-Stilwell-type data were at v/c ~ 0.005-0.03, where (v/c)^4 <= 1e-6;
   v/c = 0.005: (v/c)^4 = 6.25e-10
   v/c = 0.03: (v/c)^4 = 8.1e-7
   v/c = 0.064: (v/c)^4 = 1.68e-5
   v/c = 0.338: (v/c)^4 = 0.0131
