I experience a strange behaviour of handling the Contour and Double Contour Integral symbols \[ContourIntegral] and \[DoubleContourIntegral] in Mathematica. Whatever I try theyy behave differently than \[Integral]. Consider the following input

Integrate[f[x], x \[Element] V]
ContourIntegral[f[x], x \[Element] t]
DoubleContourIntegral[f[x], x \[Element] S]

The first statement outputs a nice mathematical notation using the \[Integral] Symbol (ignoring the obvious and clear error about the invalid integration variable). The other two, dont evaluate to any of the symbols. Even if I enter the above Contour Integrals with \[ContourIntegral] and \[DoubleContourIntegral] notation they evaluate to the ContourIntegral and DoubleContourIntegral forms. Trying TraditionalForm, HoldForm or Inactivate do not help either. Any Ideas how to convince Mathematica that the symbols stay in the original entry form?

  • $\begingroup$ @bbgodfrey It's a System` symbol with no defined meaning. The input \[ContourIntegral] f \[DifferentialD]x is interpreted as ContourIntegral[f, x], but it does not typeset the output with the special integral symbols. @ Rainer, you can control the output formatting with MakeBoxes[] or Format[]. $\endgroup$ – Michael E2 Nov 29 '20 at 2:07
  • $\begingroup$ @MichaelE2 Thanks. I misinterpreted the question. $\endgroup$ – bbgodfrey Nov 29 '20 at 2:09

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