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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 ApprovalSymlinkUrnBuilder(approval_type, subject_id, user, approval_id):
 """Build an approval symlink URN."""

    return aff4.ROOT_URN.Add("users").Add(user).Add("approvals").Add(
        approval_type).Add(subject_id).Add(approval_id)