Daas Yochid: With respect to your broad knowledge but you are wrong about bicycles. It is certainly not d’oirasa, nor is it a ‘derabbonon”. At best, it may be a “cheshas’ that if the chain breaks, one would fix it-hence much more akin to a “klei zemer’ than anything else. Certainly in Europe, children did use bicycles in their own backyard. Even your comments about mukzha are incorrect. To hold an umbrella on Shabbos is not ossur.
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