Signatures, formulas and trees

The next important concept is the notation of the signature. The signature describes the interface to the scoring function needed in our algorithm. We can derive the signature for our current example by simply interpreting each of the candidate trees' node labels as a function declaration:

number: A -> Ans minus: Ans x Ans -> Ans times: Ans x Ans -> Ans plus: Ans x Ans -> Ans div: Ans x Ans -> Ans

The symbol Ans in the abstract result domain. In the following,

**Σ**denotes the signature,**T_Σ**the set of trees over the signature Σ.