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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 load_schema(schema_ref, # type: Union[CommentedMap, CommentedSeq, Text] cache=None # type: Dict ):
 """ Load a schema that can be used to validate documents using load_and_validate. return: document_loader, avsc_names, schema_metadata, metaschema_loader """


    metaschema_names, _metaschema_doc, metaschema_loader = get_metaschema()
    if cache is not None:
        metaschema_loader.cache.update(cache)
    schema_doc, schema_metadata = metaschema_loader.resolve_ref(schema_ref, "")

    if not isinstance(schema_doc, MutableSequence):
        raise ValueError("Schema reference must resolve to a list.")

    validate_doc(metaschema_names, schema_doc, metaschema_loader, True)
    metactx = schema_metadata.get("@context", {})
    metactx.update(collect_namespaces(schema_metadata))
    schema_ctx = jsonld_context.salad_to_jsonld_context(schema_doc, metactx)[0]

    # Create the loader that will be used to load the target document.
    document_loader = Loader(schema_ctx, cache=cache)

    # Make the Avro validation that will be used to validate the target
    # document
    avsc_names = make_avro_schema(schema_doc, document_loader)

    return document_loader, avsc_names, schema_metadata, metaschema_loader