Let a clock emit a frequency of 1 Hz be moving relative to
an observer with velocity 0.866c

            t-vx/c^2
t' =     _______________
         sqrt(1-v^2/c^2)

ref (Electrodynamics, section 3)

   = t * sqrt(1-v^2/c^2)
   = 1 * 0.5
   = 0.5 seconds
   = 1 tick per 2 seconds

Consider Einstein's doppler shift, to be found in the
equation


             1-cos(phi).v/c
nu' =  nu. [________________]
             sqrt(1-v^2/c^2)


ref (Electrodynamics, section 7)
Let phi = pi/2 or 3pi/2

                     1-0
nu' =  1  .    _________________
                     0.5
     = 2 ticks per second.

So according to Einstein,

 0.5 = 2
 
Thus we have a proof by contradiction that v = 0.866c

 See also

A Google search
a5Bic.2775$TK6.87@dentist.cableinet.net