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based on an earlier version of the Wolfram Language.
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UpSet (^=)

lhs^=rhs
assigns rhs to be the value of lhs, and associates the assignment with symbols that occur at level one in lhs.
  • f[g[x]]=value makes an assignment associated with f. f[g[x]]^=value makes an assignment associated instead with g.
  • UpSet associates an assignment with all the distinct symbols that occur either directly as arguments of lhs, or as the heads of arguments of lhs.
New in 1