The sine-Gordon equation on time scales
  We formulate and discuss integrable analogue of the sine-Gordon equation on arbitrary time scales. This unification contains the sine-Gordon equation, discrete sine-Gordon equation and the Hirota equation (doubly discrete sine-Gordon equation) as special cases. We present the Lax pair, check compatibility conditions and construct the Darboux-B\"acklund transformation. Finally, we obtain a soliton solution on arbitrary time scale. The solution is expressed by the so called Cayley exponential function. 
Jan L. Cie\'sli\'nski, Tomasz Nikiciuk, Kamil Wa\'skiewicz
nlin.SI