Wolfram Language & System 10.0 (2014)|Legacy Documentation

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assigns rhs to be the value of lhs, and associates the assignment with the symbol f.


  • TagSet defines upvalues or downvalues as appropriate.
  • The symbol f in must appear in lhs as the head of lhs, the head of the head, one of the elements of lhs, or the head of one of the elements.
  • A common case is .
  • You can see all the rules associated with a particular symbol by typing ?symbol.
  • If f appears several times in lhs, then associates the assignment with each occurrence.
  • When it appears in unevaluated symbolic form, TagSet is treated as a scoping construct so that variables in nested occurrences are renamed if necessary.
Introduced in 1988