You need FFT multiplication, it seems.   
      
   Am Mittwoch, 6. Juni 2018 01:04:29 UTC+2 schrieb burs...@gmail.com:   
   > I found a system, that can do it without displaying   
   > it, in around 8.5 secs. Thats kind of fast, isn't it?   
   >   
   >    Welcome to SWI-Prolog (threaded, 64 bits, version 7.7.15)   
   >    SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software.   
   >   
   >    ?- [user].   
   >    pow(_,0,1) :- !.   
   >    pow(X,1,X) :- !.   
   >    pow(X,N,Y) :-   
   >         M is N//2, pow(X,M,A),   
   >         J is N mod 2, pow(X,J,B),   
   >         Y is (A*A)*B.   
   >    ^D   
   >   
   >    ?- time((pow(9,9,X), pow(9,X,_))).   
   >    % 159 inferences, 7.500 CPU in 8.514 seconds (88% CPU, 21 Lips)   
   >   
   > See also:   
   >   
   > Whats the fastest way to compute 9^(9^9)   
   > https://math.stackexchange.com/q/2808923/4414   
      
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