(*
 * Compute Euler's phi-function, i.e. number of number rel. prime to n.
 *
 * E.g. 8:Euler -> 4 since 1,3,5,7 are relatively prime to 8
 *)
DEF Euler AS
   [id,iota] | distl |
   EACH 
      WHILE [2,#0]|> DO [2,mod] END |
      IF [1, #1]|= THEN #1 ELSE #0 END 
   END | sum;

