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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def find_child(sexpr: Sexpr, *tags: str) -> Optional[Sexpr]: """Search for a tag among direct children of the s-expression."""

    _assert_valid_sexpr(sexpr)

    for child in sexpr[1:]:
        if _is_sexpr(child) and child[0] in tags:
            return child

    return None