Say I have an expression $a+b+a\times b$ and I define $c:= a\times b$. How do I get Mathematica to write $a+b+a\times b$ in terms of $c$, i.e. $a+b+c$?

  • $\begingroup$ Simplify[a + b + a*b, a == c/b] $\endgroup$ – Artes Sep 9 '13 at 13:38
  • $\begingroup$ What about a + b + a b /. a b -> c ? $\endgroup$ – DavidC Sep 9 '13 at 13:50
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    $\begingroup$ This is an oft-asked question with no simple answer. Really we need a canonical Q&A that addresses many variations in one place. Until that time here are some links to related questions. $\endgroup$ – Mr.Wizard Sep 9 '13 at 14:20

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