\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\\ [a_n,...,a_1] -> (a_n)n!+...+(a_1)1!.
\\ Value of Cantor factorial representation.
\\ 1168 Remmert/Ullrich, 147.
t_cantorfacval (a) ={my (n=#a);
vecsum(apply(i->a[i]*(n-i+1)!, t_numbers(n)))}

\\ 24641 Allouche/Shallit, 71.
\\ The numeration system is a strictly increasing
\\ function u: N --> N with u(0)=1.
t_greedyrep (n,u) = {my (t,A,p,a);
if (!n, return ([]));
t=0; A=[];
while (u(t)<=n,t++); t--;\
forstep (i=t,0,-1,p=u(i); a=floor(n/p);\
A=concat(A,[a]); n-=(a*p)); A}

t_realadic (x,b,maxdigits=100) = {my (n,a,v,i);
n=a=floor(x);  v=[]; i=0;
while ((x>a)&&(i<maxdigits), x=b*(x-a);\
a=floor(x); v=concat(v,[a]); i++);
[digits(n,b),v]}