Given e.g.
f := a[1]*a[2]+a[1]*a[3]+a[2]*a[3]
Now we want to substitute a[i]->i, I tried
applyrule(a[i] = i, f) applyrule(a =[seq(i, i = 1 .. nops(a))], f)
and replace "applyrule" above with "subs" and "algsubs" commands. But none works.
Any idea?