［１］ｘ^2−ｄｙ^2＝±１→（ｘ^2＋ｄｙ^2）^2−ｄ（２ｘｙ）^2＝１

［２］ｘ^2−ｄｙ^2＝±２→｛（ｘ^2＋ｄｙ^2）／２｝^2−ｄ（ｘｙ）^2＝１

［２］ｘ^2−ｄｙ^2＝４

２｜ｘ→｛（ｘ^2−２）／２｝^2−ｄ（ｘｙ／２）^2＝１

not ２｜ｘ→｛ｘ（ｘ^2−３）／２｝^2−ｄ（ｙ（ｘ^2−１）／２）^2＝１

［４］ｘ^2−ｄｙ^2＝−４

→（ｘ^2＋２）／２｛（ｘ^2＋２）^2−３｝^2−ｄ（ｘｙ／２）｛（ｘ^2＋２）^2−１｝^2＝１

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