<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def concat_ast(asts: Sequence[DocumentNode]) -> DocumentNode: """Concat ASTs. Provided a collection of ASTs, presumably each from different files, concatenate the ASTs together into batched AST, useful for validating many GraphQL source files which together represent one conceptual application. """

    return DocumentNode(
        definitions=list(chain.from_iterable(document.definitions for document in asts))
    )