package Simultaneous is
        procedure Solve(A,B,C,D: in Integer; P,Q:in Float; X,Y: out Float);
        --# derives X,Y from A, B, C, D, P, Q;
        --# post Float(A) * X + Float(B) * Y = P and
        --#      Float(C) * X + Float(B) * Y = Q;
end Simultaneous;