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  "body": "\n## Definition\n\nLet $A$ be a [[set|0SJ3RX9TXA]] and let $x$ be an object.\nThe object $x$ is an element of $A$, written $x \\in A$, when $A$ contains $x$.\nOtherwise, $x$ is not an element of $A$, written $x \\notin A$.\nThe proposition $x \\notin A$ is the negation of $x \\in A$.\n\n## Remarks\n\nOther phrases for $x \\in A$ are \"$x$ is a member of $A$\", \"$x$ belongs to $A$\" and \"$x$ is in $A$\".\nFor $A = \\{1, 2, 3\\}$, $2 \\in A$ and $4 \\notin A$.\nAn element of a set can itself be a set: $\\{1\\} \\in \\{\\{1\\}, 2\\}$, but $1 \\notin \\{\\{1\\}, 2\\}$.\n\n## Explanations\n\n### L1 human\n\nThe symbol $\\in$ asks one yes or no question: is this object in the set?\nFor the set of even numbers, $6 \\in$ the set and $7 \\notin$ the set.\n",
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