def _get_nton_name(nton, prefix=''):
    """Given the number of strains in which a polymorphism/substitution is found, give the appropriate SFS name."""
    named = {1: 'single', 2: 'double', 3: 'triple', 4: 'quadruple', 5: 'quintuple'}
    middle = named.get(nton, str(nton) + '-')
    return prefix + middle + 'tons'