It's not hard to understand, it's simply incorrect.
Once again, use exactly what you wrote and test it to see if it is true, or false. Let's make up something, and refer to it as A. It MUST logically be possible, or not possible. (A, or not A) That's logic 101 right? It's either A, or not A. It's either BLACK or NOT BLACK, etc. You with me?
Let's plug in "impossible" for A. (Possible or not possible...we're choosing not possible as a test of your claim)
1. A is a square circle (an impossibility)
2. It's impossible to prove A exists. (from your claim above) T
herefore A is possible. (from your claim above) Which contradicts #1. A is NOT possible.
To be correct you would simply state.
1. A is a square circle
A by definition is a contradiction. (contradictions are not real).
You know why there was the phrase "you cannot prove a negative" right? It was an attempt to clarify what you are doing. You even do it in the response above. Let A = nothing. Since we cannot PROVE nothing exists, it's therefore possible NOTHING exists (according to your claim above). That's obviously false, why are you not acknowledging that? Showing a contradiction in 2-3 steps, I don't know how much more simple it can be broken down for you.