{"schema_version":"ocme-site-results-v1","locale":"en","page_type":"derivations","facts":{"questions":36000,"reviewed":36000,"display_candidates":0,"knowledge":302,"guides":299,"paths":59,"batches":360,"families":1441,"atlas":302,"core":80,"evidence":9,"formal_evidence":5,"formal_subjects":4,"lean_files":6,"lean_toolchain":"leanprover/lean4:v4.30.0","question_state":"candidate","english_state":"ai_candidate","question_Lean":"NOT_RUN","canonical_truth_promotion":false},"filters":{"q":"mko-real-number"},"kind":"guides","total":1,"pages":1,"page":1,"entries":[{"id":"derivation-mko-real-number-01","title":{"zh-Hant":"實數：在 Cauchy 完備化中證明「循環的 9」與有理數 1 是同一個實數","en":"Real number: proving in the Cauchy completion that 'repeating nines' and the rational 1 are the same real"},"summary":{"zh-Hant":"在以有理數 Cauchy 序列的等價類建構的實數中（有理數 q 嵌入為常數列的類 ι(q)），令 a_n=1−10^{−n}（n≥1），即有限小數 0.9、0.99、0.999 等。證明 (a_n) 是 Cauchy 序列，且與常數列 1 等價，所以 [(a_n)]=ι(1)；證明 ι 是單射，因此有限小數 0.999=999/1000 所表示的實數不等於 1；並說明有限小數 0.375=3/8 是有理數，在 ℝ 中就是 ι(3/8)。","en":"In the reals constructed as equivalence classes of Cauchy sequences of rationals (a rational q embedded as the class ι(q) of its constant sequence), let a_n=1−10^{−n} (n≥1), the finite decimals 0.9, 0.99, 0.999 and so on. Prove that (a_n) is a Cauchy sequence equivalent to the constant sequence 1, so [(a_n)]=ι(1); prove that ι is injective, so the real denoted by the finite decimal 0.999=999/1000 is not 1; and show that the finite decimal 0.375=3/8 is rational and is ι(3/8) in ℝ."},"mko_ids":["mko-real-number"]}],"title":"Concept derivation guides"}