I'm trying to understand the various ways to do pattern matching. The problem is that sometimes the patterns seem to matched against a normal form that's different from the one displayed. For example can somebody explain to me why the last pattern match fails below?

> patmatch((1/2)*Zeta+(1/3)*Zeta^5, conditional(Zeta^n::posint*y::anything+z::anything, n >= 3), 's'); s;
true
[n = 5, y = 1/3, z = (1/2)*Zeta]
> patmatch(Zeta^2+(1/3)*Zeta^5, conditional...

I'm trying to use define but get unexpected behavior. Say I want to declare that the map phi is additive. I would try this

define('phi',phi(x::`+`)=map(phi,x));

But if I do phi(x+y) now, I get a warning about an infinite recursion. I get an indication of what the problem is if I define instead

define('phi',phi(x::`+`)=op(x));

Now phi(x+y) produces "x+y" rather than "x,y", so somehow the sum is considered atomic. Can somebody explain this to me?