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.
Introduced in 1988