@salim-barzani I suppose that it may be important to some members to know that you might delete your own Question threads, even after they have responded.

@Carl Love I have a hazy recollection that double-quote strings were already in MapleV R5.

@romanrieme You can index into a VectorCalculus Vector in the usual ways, using square brackets.

You can access the value. You can assign it to some other name. You can replace the element's value. And so on.

Download VC_Vector_indexing.mw

Did you delete any of your own previous Question thread on ODEs?

I mean, the threads on Hirota Bilinear Form? Did you yourself delete any of those?

Do you have a question to accompany that expression?

ps. I've deleted the three other duplicate postings of your expression.

@salim-barzani You could always try (re)reading the User Guide, and its sections on input.

There's a section there on 1-D Math Input, btw.

@salim-barzani As mentioned, the errant characters in your 2D Input are hidden. That means that they are not visible. So, yes, it looks the same. But they are actually different.

Your Maple has the exact same 1D input capabilities as mine.

If you have too many difficulties working with 2D Input you could switch entirely to 1D notation (using Execution Groups rather than Document Blocks). You could also use Worksheet mode rather than Document mode. And you can set all these things as default preferences.

Or, if you only have 2D Input troubles like this now and then you could troubleshoot using the lprint technique I described.

@mmcdara 

substring(x,1)

@Ronan I applied the lprint command to the sets that were being used.

Line-printing expressions is a useful way to get a plaintext view of most structures. It lets you see what is actually there.

Another handy variant I seem to use often is lprint of indets(...,name) which can line-print just the names. That can be useful in detecting accidental presence of, say, X[i] along with X__i.

Another handy 2dmath-debugging trick is to lprint the results of indets(...,function), which can reveal subexpressions where multiplication symbols (or space for implicit multiplication) was accidentally omitted, eg. x(y+2) the function call instead of x*(y+2).

ps. For shorter expressions I sometimes use the right-click context menu to change the 2D Input to 1D Maple Notation. For larger examples I prefer often those targeted queries.

@salim-barzani The people capable of resolving your problem appear very much to read everything, including new Replies on older Question threads. (There are a few ways in which such recent additions can bubble to the top of a few feeds.)

But if you simply spawn yet another wholly separate new Question thread on this same topic (with some additional details that you missed there and here, or could sensibly add there, or here) then it'll be flagged as a duplicate and may well be deleted. Please don't do that.

@salim-barzani Don't delete anything!

Simply add your followup refinement as a Reply to your Question, here in this Question thread.

@salim-barzani Please don't spawn even more duplicate Question threads on this, just because you haven't received here a response that is satisfactory to you.

@WD0HHU On that code, without the filename being given with absolute path, the location of the file will depend on the value returned by the Maple command currentdir().

And that depends on the OS and how Maple was launched.

Note that in M2024.1, you get a better handling of the middle root with evala(Nans) than simplify(Nans).

I have changed your Post into a Question.

In future, please submit your queries as Questions, not Posts.