# Unfamiliar output of FullSimplify [duplicate]

I got the following output of FullSimplify, when expecting to get "0".

I found no explanation of this output here. Could you please explain, what it means? That my expression equals zero when the condition $m^4 \Omega ^2 \sin ^2(\theta )+2 m r<r^2$ holds and that big fraction otherwise? Or maybe something else?

• Duplicate of mathematica.stackexchange.com/q/102259/12 In that post, also look at the linked questions on the right. Oct 24, 2017 at 12:23
• @Szabolcs not necessarily. Perhaps Piecewise in general was unknown to OP. Oct 24, 2017 at 14:46
• @LLlAMnYP This has been asked several times before. There are many practically identical questions marked as a duplicate of that one (which is why I said look at the sidebar). I agree that the answer there needs a slight updating to accommodate these better. It can't me marked as a duplicate of a post that is already closed as a duplicate. Oct 24, 2017 at 14:53
• @Szabolcs sorry, didn't read the last half of your comment \_('')_/ Oct 24, 2017 at 14:54
• @Szabolcs well I've looked through the questions, and if anything is a duplicate, it's this one: mathematica.stackexchange.com/q/109071/26956 But I reckon the suggestion to inspect the FullForm when encountering an output you don't understand is more general. Not sure if vote to leave open or nominate this link as another duplicate. Oct 24, 2017 at 15:03

my expression equals zero when the condition m4Ω2sin2(θ)+2mr<r2 holds and that big fraction otherwise?
Your assumption is correct. What you see is the typeset OutputForm of Piecewise.
What you can do, however, is to run FullForm@% after you get a result like that. The output will be something like
Piecewise[ (* stuff *) ]

then you can realize that you need to look up Piecewise.