'begin' # 8.6. sample program for united modes #
    'mode''rc'='union'('real','compl');
    'proc'qe=('real'a,b,c)[]'rc':
	#quadratic equation with real coefficients#
	'if''real'd:=b^2-4*a*c;d>0
	    'then'd:=sqrt(d)/2/a;(-b/2/a+d,-b/2/a-d)
	'elif'd=0
	    'then'-b/2/a
	'else'd:=sqrt(-d)/2/a;'real're=-b/2/a;(re'i'd,re'i'-d)
	'fi';
    'while'
	'real'a,b,c;print((newline,"the coefficients, please : "));
	read((a,b,c)); a/=0
    'do' print(qe(a,b,c))'od'
'end'