Rvs.m is a Mathematica package which contains the results for the
functions R^{(i),x}_Y (i=0,1,2; x=s,v; Y=FF,FA,FL,FH) as defined in
K.G. Chetyrkin, M. Steinhauser: "Three-loop non-diagonal current
correlators in QCD and NLO corrections to single-top-quark
production", report numbers TTP00-25, hep-ph/0012002.

For the Born and order \alpha_s result the exact formulae are
implemented.  At order \alpha_s^2 each case is represented by a
typical Pade approximant.  For the renormalization scale \mu^2 = M^2
is adopted where M is the on-shell mass.  The functions depend on the
variable v = (1-M^2/s)/(1+M^2/s).