For criss-cross reduction, you don't need to sart   
   with an extra variable t:   
      
      [f * t, g * (1 - t)]   
      
   You just start with:   
      
      [f0, f1]   
      
   Then you reduce fn by fn-1 to get fn+1, and switch   
   sides, and you get a polynomial remainder sequence:   
      
      [f1, f2]   
      
      [f2, f3]   
      
      ..   
      
      [fn, 0]   
      
   fn is the GCD, just a special case and variant of a GB   
   without any occurence of a S-polynomial (for univariate   
   polynomials S-polynomials are not need, wont happen when   
   criss-cross reducing).   
      
   Very simple and effective.   
      
   Am Donnerstag, 6. Juli 2017 19:29:33 UTC+2 schrieb burs...@gmail.com:   
   > that for GB that does a criss-cross reduction, we   
   > have the classical Euclidean GCD algorithm for   
   > univariate polynomials,   
      
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