I would like to eliminate all terms that contain the product of dxy, dwz, and dxz, i.e. the final result should read as dxy +b dwz+ c dxz. Thanks in advance for any hint.

a dxy +b dwz+ c dxz+e dxy dwz +f dxy dxz +g dwz dxz + h dxy dxz dwz
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    – rhermans
    Jun 13 '18 at 11:04
  • $\begingroup$ @user58765 Can you check the post that Carl cited and say if it helps to solve your problem? $\endgroup$
    – halirutan
    Jun 13 '18 at 22:00

From the linked question:

expr = a dxy +b dwz+ c dxz+e dxy dwz +f dxy dxz +g dwz dxz + h dxy dxz dwz;

Normal @ Series[
    expr /. v:(dxy|dwz|dxz) -> v t,
    {t, 0, 1}
] /. t->1

b dwz + a dxy + c dxz


Or this way

expr = a dxy + b dwz + c dxz + e dxy dwz + f dxy dxz + g dwz dxz + 
       h dxy dxz dwz // Expand;

prodterms = Apply[Times, Subsets[{dxy, dwz, dxz}, {2, 3}], 2]

(*   {dwz dxy, dxy dxz, dwz dxz, dwz dxy dxz}   *)

expr /. Thread[prodterms -> 0]

(*   b dwz + a dxy + c dxz   *)

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