%begin
%owninteger nextsym=4
%integer opd
opd=23
%unless 20<=opd<=nextsym+20 %then printstring(" bug1 
")
%if 20<=opd<=nextsym+20 %then opd=opd %else printstring(" bug2 
")
%unless opd>=20  %and opd<=nextsym+20 %then printstring(" bug3 
")

%endofprogram