Circled plus, minus, times and divides symbols (U+2295 through U+2298) are much too large

[Gro-Tsen]

Circled plus, minus, times and divides symbols are much too large

In Inter-4.1, the glyphs “circleplus”, “uni2296”, “circlemultiply” and “uni2298”, respectively mapped to the Unicode characters U+2295 CIRCLED PLUS, U+2296 CIRCLED MINUS, U+2297 CIRCLED TIMES and U+2298 CIRCLED DIVISION SLASH, are much too large.

Specifically, the circle is too large with respect to the central operator.

These characters are mathematical operators, and in mathematics they are written with the circle touching the outer edge of the circled operator, but no larger. A very thin margin between the operator and the circle is acceptable, but Inter uses far too much spacing.

An example of what these characters should look like is provided by the Unicode standard reference charts. Note the absence of any space between the circle and the operator.

The current glyphs used in Inter make a mathematical formula such as “x⊗y + u⊗v” look very wrong (because the circled times is so large, it makes it seem as though it is the outer operator in the formula). This is all the more confusing because there are “large” variants of the operators (such as U+2A01 N-ARY CIRCLED PLUS OPERATOR; Inter does not have it) which are supposed to be larger. Font mixing will cause these “large” operators to be, effectively, smaller than the supposedly “small” U+2295 CIRCLED PLUS and such.

The issue has raised to prominence because the social network Bluesky uses Inter as its default font on its Web interface, and many people (such as myself) wish to be able to discuss mathematics on Bluesky: this glyph problem is causing confusion and making communication around linear algebra much harder.

I would argue that other circled symbols in Inter are also too large (e.g., circled digits), but this is, of course, a matter of taste, whereas the circled operators of mathematics have a well-established shape within the field.

[thlinard]

This was supposed to have been fixed (issue #250), but it appears not. Example with the sequence B+⊕B−⊖B×⊗B⊘B⨁B⨂B (B, +, − and × are there only as reference points):

Characters

⊕ U+2295 CIRCLED PLUS ⊖ U+2296 CIRCLED MINUS ⊗ U+2297 CIRCLED TIMES ⊘ U+2298 CIRCLED DIVISION SLASH ⨁ U+2A01‎ N-ARY CIRCLED PLUS OPERATOR ⨂ U+2A02 N-ARY CIRCLED TIMES OPERATOR

Fonts

Inter, version 4.1 Iosevka, version 33.0.1 Libertinus, version 7.051

[thlinard]

Another example with STIX Two Math version 2.14, a reference math font:

[Gro-Tsen]

It has been brought to my attention that the Unicode chart for block 2200–22FF lists, on the last page, a number of standardized variation sequences, including 2295 FE00 (that is, CIRCLED PLUS followed by VARIATION SELECTOR-1) to display a circled plus with a white rim between the plus and the circle. This also goes toward suggesting that, by default, the circle should be only so large as to touch the enclosed operator but no larger.

[thlinard]

Indeed, but probably the most important thing is that, as Johannes Küster (Fonts for Mathematics) says:

Glyphs of the same kind should have the same width

So the circle should not increase the width of the operator.

[Dai-JiaLin]

the same with circled numbers from 1-10

[thlinard]

Another solution, if the choice to encode these glyphs at positions U+2295-U+2298 (and the circled numbers too) does not stem from a desire to create characters useful in mathematics but simply to make this design accessible:

1. Remove the Unicode codes from these glyphs.
2. Include them in a nalt feature (https://helpx.adobe.com/fonts/using/open-type-syntax.html#nalt), which is an OpenType feature specifically designed for this purpose.