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- $ a \\\subset \\\left[ {a;b} \\\right].$
- $ \\\left\\\{ a \\\right\\\} \\\subset \\\left[ {a;b} \\\right].$
- $ a \\\in \\\left( {a;b} \\\right].$
- $ \\\left\\\{ a \\\right\\\} \\\in \\\left[ {a;b} \\\right].$