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  "body": "\n## Summary\n\nA cardinal function in topology assigns a [[cardinal number|0EBACQFAZW]] to each topological space so that homeomorphic spaces get the same cardinal.\nStandard examples are the weight, the density, the character and the cellularity.\nCardinal functions turn countability properties into numbers, so that, for example, [[second-countable|03PPNCM9GG]] means weight at most $\\aleph_0$.\nMany theorems of general topology are inequalities between cardinal functions.\n\n## Explanations\n\n### L1 human\n\nA cardinal function measures the size of some feature of a space.\nThe weight counts how many open sets you need in a base, and the density counts how many points you need in a dense subset.\nFor the real line, both numbers are countable: open intervals with rational endpoints form a base, and the rationals are dense.\nFor an uncountable set with the discrete topology, both numbers equal the number of points.\n",
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