Transformer is a function from seq of symbols to seq of symbols.
For example, truth table is exactly similar kind of function from variables to [True, False] alphabet.
Transformer can represent some very complex logical operations, and per this article is turing complete: https://arxiv.org/abs/1901.03429, meaning any computable function, including theorem prover can be represented as transformer.
Another question is if it is feasible/viable/rational to build transformer for this? My intuition says: no.