best cryptic crossword clue ever

From a puzzle in the office kitchen today:

#21 down: 1. x_i ∀y - f. Or, how one traverses the Cartesian plane due north, for example

( answer )

street photography

The BBC's "Viewfinder" blog writes about the importance of street photography:

"For me, with my photographer's hat on, what keeps me doing this is a belief that one of photography's core purposes is to discover poetic moments in everyday life. From the invention of the medium, nosey parkers, journalists, voyeurs, and poets have used cameras to show us that this world is an intrinsically fascinating place to live in."