Less-than or equal to
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About the less-than or equal to
Plain < and > first appear in Thomas Harriot’s Artis Analyticae Praxis, printed in 1631, ten years after his death. Adding “or equal to” took longer. John Wallis tried a single bar above the sign in 1670, and in 1734 Pierre Bouguer, a French mathematician, wrote two bars underneath, the form still seen as ≦. Today’s ≤ keeps one bar below.