Question: In Alchemy, the rules for what kinds of cards can replace a trashed card are governed by the following, somewhat ambiguous wording:

> 
> Adding coins to a cost doesn't affect [potion] being in the cost or
>  not. If [potion] was in the cost, it still is; if it wasn't, it still
>  isn't.
> 
> 
> 

The rules then present an example with Remodel card. However, the Remodel card says:

> 
> Gain a card costing *up to* two more . . .
> 
> 
> 

The Governor card wording is:

> 
> Gain a card costing exactly one (or two [if you're the player playing
>  the card]) more.
> 
> 
> 

So, for the player who played the Governor card, it is clear from the remodel example that a card costing exactly 2 coins must be replaced by a card costing exactly 4 coins with no potion.

However, what about a card costing exactly 2 coins and a potion? If trashed, must it be replaced with a card costing exactly 4 coins and a potion? Or could it also be replaced by a card costing exactly 4 coins (but with no potion)?

Answer: 
@JHaasie77's answer is spot on, I just want to add another way to think about it that grew too long for a comment.

Costs with potions are like complex numbers, with the potion cost corresponding to the imaginary part. The now-defunct Isotropic online Dominion server handled this quite nicely using `p` to designate potions. If you played 3 Coppers and 2 Potions, Isotropic would report the amount of money you have to spend as `3+2p` (or something like that).

Using this analogy, University costs `2+p`, and `Governor`ing a University calls for adding exactly 1 (or 2 if you're the player playing the card) to the cost. Thus the card you gain from trashing a University to a Governor must be exactly `2+p+1 = 3+p` (or if you played the Governor, `2+p+2 = 4+p`).

The analogy isn't perfect for cards like Remodel specifying "costing up to `x` more", but it's workable. The "up to" applies to both coin part and to potion part. Remodeling a University lets you gain a card costing up to `2+p+2 = 4+p`, so up to `4` in coin cost, and up to `1` in potion cost.
'Up to' means you can exchange a card with potion in the cost into a card that does or does not not have a potion in the cost, but you can **not** remodel a card with no potion in the cost into one that does. Remodel says "up to". You may Remodel a Golem into a Gold, or Remodel an Apothecary into a Golem. 

If the card says "exactly" like Governor, the card to be gained has to have the same number of potions in the cost, and the specified cost in coins. If you play Governor, you can trash University, and the only possible card you can get in exchange is Golem, as it's the only card that costs exactly 2 more than University.