the technical symbol they represent. The "micro sign" (U+00B5, µ) is obviously inherited from ISO 8859-1, but the origin of the others is less clear. Other Greek glyph variants encoded as separate characters include the lunate sigma Ϲ ϲ contrasting with Σ σ, final sigma ς (strictly speaking a contextual glyph variant) contrasting with σ, The Qoppa numeral symbol Ϟ ϟ contrasting with archaic Ϙ ϙ. Greek letters assigned separate "symbol" codepoints include the Letterlike Symbols ϐ, ϵ, ϑ, ϖ, ϱ, ϒ, and ϕ (contrasting with β, ε, θ, π, ρ, Υ, φ); the Ohm symbol Ω (contrasting with Ω); and the mathematical operators for the product ∏ and sum ∑ (contrasting with Π and Σ). Roman numerals Unicode has a number of characters specifically designated as Roman numerals, as part of the Number Forms range from U+2160 to U+2183. For example, Roman 1988 (MCMLXXXVIII) could alternatively be written as ⅯⅭⅯⅬⅩⅩⅩⅧ. This range includes both upper- and lowercase numerals, as well as pre-combined glyphs for numbers up to 12 (Ⅻ for XII), mainly intended for clock faces. The pre-combined glyphs should only be used to represent the individual numbers where the use of individual glyphs is not wanted, and not to replace compounded numbers. For example, one can combine Ⅹ with Ⅰ to mean Roman numeral eleven (ⅩⅠ), so U+216A (Ⅺ) is canonically equivalent to ⅩⅠ. Such characters are also referred to as composite compatibility characters or decomposable compatibility characters. Such characters would not normally have been included within the Unicode standard except for compatibility with other existing encodings (see Unicode compatibility characters). The goal was to accommodate simple translation from existing encodings into Unicode. This makes translations in the opposite direction complicated because multiple Unicode characters may map to a single character in another encoding. Without the compatibility concerns the only characters necessary would be: Ⅰ, Ⅴ, Ⅹ, Ⅼ, Ⅽ, Ⅾ, Ⅿ, ⅰ, ⅴ, ⅹ, ⅼ, ⅽ, ⅾ, ⅿ, ↀ, ↁ, ↂ, ↇ, ↈ, and Ↄ; all other Roman numerals can be composed from these. See also IDN homograph attack Unicode equivalence Homoglyph ASCII art References Unicode