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  "body": "\n## Summary\n\nThe ordinal sum of two partially ordered sets places the second one entirely above the first.\nInside each part the order is unchanged, and every element of the first part is below every element of the second.\nIt is also called the linear sum or series composition, and it extends the addition of [[ordinal numbers|0YSCSX5YZC]].\n\n## Explanations\n\n### L1 human\n\nStack two posets on top of each other, like two floors of a building.\nEverything on the lower floor is below everything on the upper floor.\nStacking a single point on top of a two-element antichain gives a \"V\" shape turned upside down, with the point as the top.\nThe order of stacking matters: a point below the antichain gives a different poset.\n",
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