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based on an earlier version of the Wolfram Language.
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Which

Which
evaluates each of the in turn, returning the value of the corresponding to the first one that yields True.
  • If any of the evaluated by Which give neither True nor False, then a Which object containing these remaining elements is returned unevaluated. »
  • You can make Which return a "default value" by taking the last to be True.
Which can be maintained in symbolic form:
Conditions are evaluated until one is found that is neither True nor False:
Use True for an else clause that always matches:
Define a piecewise function:
Expand it to use Piecewise:
Do symbolic operations:
Use Which rather than a nested if-then-elsif chain:
Use PiecewiseExpand to convert Which to Piecewise:
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