predicates
	require(real,real,real)
	reply(real,real,real)

clauses
	require(A,_,_):-A=0,!,
		       write("A inputing is wrong").
	require(A,B,C):-D=B*B-4*A*C,reply(A,B,D).
	reply(_,_,D):-D<0,write("No solution"),!.
	reply(A,B,D):-D=0,
		      write("One solution "),
                      X=-B/(2*A),write(X),!.
	reply(A,B,D):-X1=(-B+sqrt(D))/(2*A),
	              X2=(-B-sqrt(D))/(2*A),
	              write(" X1= ",X1),nl,
	              write(" X2= ",X2),nl.
goal
 	write("a= "),readreal(A),nl,
 	write("b= "),readreal(B),nl,
	write("c= "),readreal(C),nl,
 	write("the results are:"),nl,
	require(A,B,C).