[Groff] On the glyphs `~=' and `|='

[Werner LEMBERG]

Some thoughts on the glyphs `~=' and `|='; please tell me if you
disagree with my research below.

  `~=': In the Unix Text Processing book, it is called
        `approx. equal', but the glyph displayed is definitely wrong.

        The Unicode charts display for U+2245 APPROXIMATELY EQUAL TO
        an equal sign and a wavy line stacked vertically; groff uses
        `=~' for this glyph (PS glyph name `congruent').

        groff's groff_char.man page gives two wavy lines stacked
        vertically.  An alias is the glyph name `~~'.

        The original CSTR 54 document doesn't contain this glyph.

        The AGL assigns the PS glyph name `approxequal' to U+2248
        ALMOST EQUAL TO which is what groff uses.

        Conclusion: `~=' is a misleading glyph name.  For backwards
                    compatibility, I will leave it as-is, so it is not
                    `approx. equal' but `almost equal to'.

  `|=': Missing in the Unix Text Processing book.

        Missing in groff 1.18.1.  I'll add it right now.

        CSTR 54 stacks a minus sign with a wavy line (using a small PS
        subroutine to synthesize the shape); this is U+2243
        ASYMPTOTICALLY EQUAL TO.


    Werner