How do I graph the interference pattern for the level surface given by

Intensity = Cos[4*Pi/d(x + y)] + Cos[4*Pi/d(y + z)] + Cos[4*Pi/d(-y +
z)] + Cos[4*Pi/d(x - y)] + Sin[4*Pi/d(x + y)] - Sin[4*Pi/d(y + z)] -
Sin[4*Pi/d(-y + z)] - Sin[4*Pi/d(x - y)]

where d is an arbitrary number in microns, in Mathematica.  

This isn't homework, i'm simply trying to get this thing to work.

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Request for Question Clarification by hedgie-ga on 28 Jun 2006 06:38 PDT

If d is a number, not a function, then

d(y + z)

means d*(x+z)

??