differentiation by Histocrat

#!ruby -p
gsub(/(\D)?(\d+)(x(\^(\d+))?)?/){[$1,$4?[$2.to_i*e=$5.to_i,:x,([:^,e-1]if e>2)]:$2]if$3}

Note that non-ascii characters in the above source code will be escaped (such as \x9f).

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