# Mathematica can't simplify disguised expression [duplicate]

When I simplify the following quartic polynomial with a linear constraint;

Simplify[x y z a + x y z b , a + b + c == 0] // Expand

I get what to me seems like the most simple form

-c x y z

Now I disguise the problem a little;

Simplify[Subscript[k, 1]\[CircleDot]Subscript[k, 3] Subscript[k, 2]\[CircleDot]Subscript[\[Epsilon], 3] Subscript[k, 2]\[CircleDot]Subscript[\[Epsilon], 4] Subscript[\[Epsilon], 1]\[CircleDot]Subscript[\[Epsilon], 2] + Subscript[k, 1]\[CircleDot]Subscript[k, 3] Subscript[k, 2]\[CircleDot]Subscript[\[Epsilon], 3] Subscript[k, 3]\[CircleDot]Subscript[\[Epsilon], 4] Subscript[\[Epsilon], 1]\[CircleDot]Subscript[\[Epsilon], 2], Subscript[k, 2]\[CircleDot]Subscript[\[Epsilon], 4] + Subscript[k, 3]\[CircleDot]Subscript[\[Epsilon], 4] + Subscript[k, 1]\[CircleDot]Subscript[\[Epsilon], 4] == 0] // Expand

And Mathematica no longer makes any simplification, I just get out what I put in

Subscript[k, 1]\[CircleDot]Subscript[k, 3] Subscript[k, 2]\[CircleDot]Subscript[\[Epsilon], 3] Subscript[k, 2]\[CircleDot]Subscript[\[Epsilon], 4] Subscript[\[Epsilon], 1]\[CircleDot]Subscript[\[Epsilon], 2] + Subscript[k, 1]\[CircleDot]Subscript[k, 3] Subscript[k, 2]\[CircleDot]Subscript[\[Epsilon], 3] Subscript[k, 3]\[CircleDot]Subscript[\[Epsilon], 4] Subscript[\[Epsilon], 1]\[CircleDot]Subscript[\[Epsilon], 2]

I do have some rules defined for \[CircleDot] which make it like an inner product, but I don't think that should affect this situation.

To me, I have asked Mathematica to do exactly the same thing twice. Why can it not do it the second time?

• Could you get rid of the fancy formatting? Especially subscripts etc are a pain to parse quickly on this site. Jun 1, 2016 at 14:08
• Try also Simplify[x y z d + x y z e , d + e + c == 0]... Jun 1, 2016 at 14:22
• I don't think Simplify is familiar with inner products. Jun 1, 2016 at 15:02
• Well the formatting appears to me to be what is causing the problem Yves. Ah that's interesting Marius thanks for the extra example. So do you know how to teach Mathematica that the one with only one term is more simple? Daniel, I'm not asking it simplify the inner products
– Jojo
Jun 1, 2016 at 15:07
• Using VOISimplify: VOISimplify[{Subscript[k, 1], Subscript[k, 2]}, exprFromOP, assumptionFromOP] gives desired result. Jun 1, 2016 at 16:50