At the top of the vertical in this problem, the point P was an airplane in flight.
An airplane in flight, high above the clouds—but the sky was empty. They weren’t in the flight path from the airport today. Cirrus streaked the patch of blue that he could see through the plate-glass front window of the cafe, over the red-brick storefronts. Those feathery strokes might be the fringe of a system whirling north to Duluth, and thence across the North Atlantic, through the shoals of icebergs to the dark gates of the Neva: to the city where his parents had grown up, years and miles from where he had been born.
Erika’s fingertip on his sleeve reminded him to come back to earth, and to subtract the poetry.