The equals sign with a slash through it (≠) — used in mathematics since at least Euler's era, the source of a whole family of negated-relation symbols, and left out of ASCII, which is why code uses != instead. Click any symbol to copy it instantly.
The not equal sign (≠, U+2260) combines the equals sign with a diagonal slash — Unicode's own decomposition shows it as literally “=” plus a combining slash overlay (U+0338), the same mark that produces a whole family of negated relations: ≁, ≉, ≢, ≮, ≯. The slash-negation convention is a distinct, later story from Robert Recorde's 1557 invention of “=” itself — the earliest known written use traces to Leonhard Euler's 18th-century correspondence, though historians of mathematics are careful to say the symbol was used by Euler, not necessarily invented by him. Because ASCII never allocated a slot for ≠, programming languages substituted their own stand-ins — != in C-family languages, <> in SQL and Pascal, ~= in Lua and MATLAB, /= in Fortran and Haskell — which is why the math symbol and the code you actually type are almost never the same character.
The math symbol, and the ASCII stand-ins different programming languages adopted since ≠ itself was never part of the character set.
≠ isn't alone — the same diagonal-slash overlay negates several other relation symbols in Unicode's Mathematical Operators block.
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