2011/5/23 Wolfgang Schuster <schuster.wolfgang@googlemail.com>

> Please send a complete example!
>

Sure:

\startMPdefinitions{solvers}
\stopMPdefinitions

\starttext
Hello.
\stoptext
or this:

\startMPdefinitions{solvers}
def draw_problem (expr p, q, r, s, show_lables)=
begingroup ; save x, y, a, b, c, d, e, f, g, h ;
z11=z42=p ; z21=z12=q ; z31=z22=r ; z41=z32=s ;
a=x12-x11 ; b=y12-y11 ; c=x22-x21 ; d=y22-y21 ;
e=x32-x31 ; f=y32-y31 ; g=x42-x41 ; h=y42-y41 ;
z11=(x11, y11) ; z12=(x12, y12) ;
z13=(x12-b, y12+a) ; z14=(x11-b, y11+a) ;
z21=(x21, y21) ; z22= (x22, y22);
z23=(x22-s,y22+c) ; z24=(x21-d, y21+c) ;
z31=(x31, y31) ; z32=(x32, y32) ;
z33=(x32-f, y32+e) ; z34=(x31-f, y31+e);
z41=(x41, y41) ; z42=(x42, y42) ;
z43=(x42-h,y42+g) ; z44=(x41-h,y41+g) ;
pickup pencircle scaled .5pt ;
draw z11--z12--z13--z14--cycle ; draw z11--z13 ; draw z12--z14 ;
draw z21--z22--z23--z24--cycle ; draw z21—z23 ; draw z22—z24 ;
draw z31--z32--z33--z34--cycle ; draw z31—z33 ; draw z32—z34 ;
draw z41--z42--z43--z44--cycle ; draw z41—z43 ; draw z42—z44 ;
z1=0.5[z11,z13] ; z2=0.5[z21,z23] ;
z3=0.5[z31,z33] ; z4=0.5[z41,z43] ;
draw z1--z3 dashed evenly ; draw z2--z4 dashed evenly ;
z0=whatever[z1,z3]=whatever[z2,z4] ;
mark_rt_angle (z1,z0,z2);
if show_labels>0:
draw_problem_labels ;
fi;
endgroup ;
enddef ;
\stopMPdefinitions

\starttext
Hello.
\stoptext

Result is the same.

Vedran