fib 0 = 0;
 fib 1 = 1;
 fib n = fib (n-2) + fib (n-1) if n>1;

 fib n = fibs (0,1) n with
   fibs (a,b) n = if n<=0 then a else fibs (b,a+b) (n-1);
 end;

 map fib (1..20);

 queens n = search n 1 ;
   safe (i,j) p  = ~any (check (i,j)) p;
   check (i1,j1) (i2,j2)
                 = i1==i2 || j1==j2 || i1+j1==i2+j2 || i1-j1==i2-j2;
 end;

 primes = sieve (2..inf) with
   sieve (p:qs) = p : sieve (| q = qs; q mod p ) &;
 end;

 gauss_elimination x::matrix = p,x
 when n,m = dim x; p,_,x = foldl step (0..n-1,0,x) (0..m-1) end;
 
 step (p,i,x) j
 = if max_x==0 then p,i,x else
     // updated row permutation and index:
     transp i max_i p, i+1,
     ;
 x; gauss_elimination x;

 expand = reduce with
   (a+b)
*c = a
*c+b
*c;
   a
*(b+c) = a
*b+a
*c;
 end;
 
 factor = reduce with
   a
*c+b
*c = (a+b)
*c;
   a
*b+a
*c = a
*(b+c);
 end;
 
 expand ((a+b)
*2); // yields a
*2+b
*2
 factor (a
*2+b
*2); // yields (a+b)
*2