\startMPpage[instance=3Ddoublefun]

% Inspired by and largely copied from Donald Knuth's = METAFONT dangerous bend glyph

h=3D11;

u=3Dh/15;

w=3Dh*8.5/4.6;

heavyline=3D2;

y1=3D25/27h;

x4=3D0;

x1+x1=3Dx1a+x1b=3Dx4b+x2a=3Dx4+x2=3Dx4a+x2b=3Dx3b+x3a=3Dx3+x3=3D= w;

x4a=3Dx4b=3Dx4+u= ; x3b=3Dx1a=3Dx1-2u;

y4+y4=3Dy4a+y4b=3Dy3b+y1a=3Dy3+y1=3Dy3a+y1b=3Dy2b+y2a=3Dy2+y2=3D= 0;

y1a=3Dy1b=3Dy1-2/27h; = y4b=3Dy2a=3Dy4+4/27h;

path signboard; signboard :=3D = z1a..z1..z1b---z2a..z2..z2b---

z3a..z3..z3b---z4a..z4..z4b---cycle; % = signboard

fill signboard = withcolor yellow;

x10=3Dx11=3Dx12=3Dx13=3D(.5w-u); = x14=3Dx15=3Dx16=3Dx17=3Dw-x10;

y10=3Dy14=3D28/27h+epsilon; = y13=3D-h*(6.6/4.1);

z11=3D(z10..z13) intersectionpoint = (z1a{z1a-z4b}..z1{right});

y15=3Dy11; y16=3Dy12=3D-y11; = y17=3Dy20=3Dy21=3Dy13;

path toppost; toppost :=3D z1 -- z11 -- z10 -- z14 -- z15 -- = cycle;

path = bottompost; bottompost :=3D z3 -- z16 -- z17 -- z13 -- z12 -- = cycle;

fill toppost = withcolor .5white;

fill bottompost withcolor .5white;

draw signboard;

draw z11--z10--z14--z15; draw z12--z13; draw = z16--z17; % signpost

x20=3Dw-x21; x21-x20=3D16u; draw z20--z21; % ground = level

x38=3Dw-x31; = x38-x31=3D8u; x32=3Dx34=3Dx38; x31=3Dx35=3Dx37;

y31=3D-y38=3D12/27h; y32=3D-y37=3D9/27h; = y34=3D-y35=3D3/27h;

pickup pencircle scaled heavyline;

draw z32{z32-z31}..z34---z35..z37{z38-z37}; % = the dangerous bend

pickup penrazor xscaled heavyline rotated = (angle(z32-z31)+90);

draw z31--z32; draw z37--z38; % upper and lower = bars

\stopMPpage

which results in:

On 27 May 2020, at 21:50, = Herbert Voss <Herbert.Voss@fu-berlin.de> wrote:

Am 27.05.20 um 21:19 schrieb Gerben Wierda:
To honour Donald Knuth, = I=E2=80=99ve use his =E2=80=98dangerous bend=E2=80=99 (with attribution = of course) in one of my publications. But I only had a low res image. Is = the code of this symbol available somewhere so I can do it proper = justice in a next edition?
Knuth used

\input manmac
\dbend
\bye

Herbert

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