pgcd(a,b):={
    local r; 
    while (b!=0){
     r:=irem(a,b);
     a:=b;
     b:=r;
    } 
    return(a);
  };
  pgcdr(a,b):={
    if (b==0) 
      return(a);
    else 
      return(pgcdr(b,irem(a,b)));
  };
  bezout(a,b):={
  //renvoie la liste [u,v,d] telle que a*u+b*v=d=pgcd(a,b) (fct iterative)
  local la,lb,lr,q,lb2;
  la:=[1,0,eval(a)];
  lb:=[0,1,eval(b)];
  lb2:=eval(b);
  while (lb2 !=0){
  q:=iquo(la[2],lb2);
  lr:=la+(-q)*lb;
  la:=lb;
  lb:=lr;
  lb2:=lb[2];
  }
  return(la);
  };
  bezoutr(a,b):={
  //renvoie la liste [u,v,d] telle que a*u+b*v=d=pgcd(a,b) (fct recursive)
  local lb,q,r;
  if (b!=0) {
  q:=iquo(a,b);
  r:=irem(a,b);
  lb:=bezoutr(b,r);
  return([lb[1],lb[0]+(-q)*lb[1],lb[2]]);
  } else 
  return([1,0,a]);
  };