def is_paired_end(solid_run):
    """Determine if a SolidRun instance is a paired-end run

    Arguments:
      solid_run: a populated SolidRun instance

    Returns:
      True if this is a paired-end run, False otherwise.

    """
    if solid_run.run_definition:
        return (solid_run.run_definition.runType == "PAIRED-END")
    else:
        for sample in solid_run.samples:
            for lib in sample.libraries:
                if lib.csfasta_f5: return True
    return False