how to change variable with new variable in some functions

Dear all maxima users,

I paste this code in maxima
---------------------------------------------------------
f[n,k] := concat('f_,n,"_",k)(s)$
df[n,k] :=
  if n=0 then 0
  else
'diff(f[2*n,k],s)=%psi*((k-1)*sqrt(n-k+2)*f[2*n,k-1]-k*sqrt(n-k+1)*f[2*n,k+1])$

atvalue(f_4_2(s),s=0,0)$
atvalue(f_4_3(s),s=0,0)$

makelist( df[2,k],k,1,3);

desolve(%, makelist(f[4,k],k,1,3) );
nonzero;
---------------------------------------------------------
and i get some function which is f_4_1(s) , f_4_2(s) and f_4_3(s)...

so when I get this function, how can I change the value s=1 and  f_4_1(0) =
%e^(-x/2)*x/2 so that i can plot those 3 functions in 3D with the variable
%psi(different angle) and x ?
-- 
Regards,

RAZIF RAZALI,
Tutor & Master Student,
Physics Department,
Faculty Of Science,
Universiti Teknologi Malaysia(UTM).
+60199393606