module top;
reg x, y;
always @(x ^ y)
$display("%d %b %b", $time, x, y);
initial begin
#1 {x, y} = 2'b00;
#1 {x, y} = 2'b01;
#1 {x, y} = 2'b10;
#1 {x, y} = 2'b11;
end
endmodule