f(a,b) = f(a +b)

[Chris Lacher]

A function f(x,y) that satisfies f(x,y) = g(x+y) for some g ? 
I asked Lou Howard and here is his response:

If you think of y as time and x as position, something of the form g(x+y)
is sometimes called a "leftward propagating wave"; but this is not much
shorter than calling a spade a spade.  [It is the general solution of the
"left-going wave equation", du/dt = du/dx.]   Can't think of anything
else.  -- Lou.


--- Chris Lacher