On an infinite plane, a robot initially stands at (0, 0) and faces north. Note that: The north direction is the positive direction of the y-axis. The south direction is the negative direction of the y-axis. The east direction is the positive direction of the x-axis. The west direction is the negative direction of the x-axis. The robot can receive one of three instructions: "G ": go straight 1 unit. "L ": turn 90 degrees to the left (i.e., anti-clockwise direction). "R ": turn 90 degrees to the right (i.e., clockwise direction). The robot performs the instructions given in order, and repeats them forever. Return true if and only if there exists a circle in the plane such that the robot never leaves the circle.