b#:=250/36pt#; a#:=150/36pt#; s#:=30/36pt#;
define_pixels(b,a,s);

beginchar (13,s#+a#+s#,b#,0);
pickup pencircle scaled .4pt;
bot z1=(good.x s,0); z5=z1+(a,0);
z3=(1/2[x1,x5],good.y b);
z4-z2=whatever*angle20; 1/2[y2,y4]=2/3[y3,y1];
z2=whatever[z1,z3]; z4=whatever[z3,z5];
draw z1..z3; draw z3..z5; draw z2..z4;
filldot z1; filldot z5; filldot z3;
labels(1,2,3,4,5); endchar;

end

def A(expr alpha)= "alpha "&decimal alpha;
beginchar (begingroup charcode:=charcode+1;charcode endgroup,s#+a#+s#,b#,0);
pickup pencircle scaled .4pt;
bot z1=(good.x s,0); z5=z1+(a,0);
z3=(1/2[x1,x5],good.y b);
z2=alpha[z1,z3]; z4=alpha[z5,z3];
draw z1..z3; draw z3..z5; draw z2..z4;
filldot z1; filldot z5; filldot z3;
labels(1,2,3,4,5); endchar; enddef;

A(1-1/sqrt2); % this makes area above bar = area below bar
for alpha=.2 step .05 until .5+10epsilon: A(alpha); endfor
end