A real oddity, but there's no option but to allow them since hand operated bikes and trikes and treadle operated trikes have been around for a very long time.
Treadle operated ones are very rare, though seen at odd times in Germany in use by elderly people with limited physical abilities. Hand operated ones, usually semi-recumbent and mostly using a rowing action, are used by some disabled people and the odd enthusiast who insists the action is better than conventional pedalling.
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