Just wondering why

restart;
x:=2*{};
has(x,{})

Clearly {} is special. But is there a way to make it return true? 

Maple's infolevel is very nice feature, good for learning.

But I'd like to see more steps/info sometimes. Using infolevel set to max 5, does not show everything I like to see. Is there a way to print more info?

This is what I am   interested in. dsolve goes into Kovacic algorithm to solve second oder ODE. This algorithm is general algorithm to solve second oder linear ODE. 

https://www.sciencedirect.com/science/article/pii/S0747717186800104

restart;
infolevel[dsolve]:=5;
ode:=x^2*diff(diff(y(x),x),x)+x*diff(y(x),x)+(x^2-1/4)*y(x)=0;
dsolve(ode)

Changing printlevel to high value, does not really help here. It just prints lots of stuff I am not interested in.

What othere options are there to show more information about flow of logic, like the above?

I do not even know how to trace Kovacic code in Maple, since do not know what function/proc it is in without having to step though dsolve, which could take very long time to reach this specfic proc.

Is it possible to have Maple print the name of each proc it enter and leaves as it runs? That will be very useful addition added to printlevel. 

I have set of assumptions. The set happend to be empty at  time I used it. I forgot to change the set to list when calling assuming. This cased 'numeric exception: division by zero'
 

Is this normal and expected?

restart;
u1:=-ln(csc(x)-cot(x));
the_assumptions_on_x:={};
`assuming`([simplify(u1)],[the_assumptions_on_x])

Error, (in assuming) when calling 'signum'. Received: 'numeric exception: division by zero'
 

I fixed my code to use list at time of the call and the error went away

restart;
u1:=-ln(csc(x)-cot(x));
the_assumptions_on_x:={};
`assuming`([simplify(u1)],convert(the_assumptions_on_x,list))

The question is, why passing {} caused division by zero? 

Maple 2020.1

I found there is assume=[...] syntax. So I changed my code to use it, instead of .... assuming 

Now I find that some tests fail.  Should assuming and assume not give same result?

restart;
sol :=y(x)^(1/2) = -1+2*exp(x):
ode:=diff(y(x),x)-2*y(x) = 2*y(x)^(1/2):

odetest(sol,ode) assuming x::real, x>0

gives 0

but

odetest(sol,ode,assume=[x::real, x >0])

does not give zero. Please see screen shot below.

Reason I changed, since I started saving assumptions to use in a list. So it was easier to use assume=[....] than assuming ...., since assuming wants expression sequence in front of it and I did not know how to convert the list of assumptions I have collected to an expression sequence on the fly to use assuming, otherwise I would not have changed the code.

But my question is: Should both give same result? Why is the result different?

Help says

The assume routine sets variable properties and relationships between variables. Similar functionality is provided by the assuming command.

I am probably not using assume= correctly.   I thought I could use the same thing I had on assuming, just put it in a list. 
 

This happens each time I run a long loop.  (2,500 iterations, which takes about 3 hrs to complete)

Maple always hangs (it does not time out on odetest() ). But my question is not about this (as this is something I have to deal with for long time now and mentioned it before many times. May be one day Maplesoft will fix this). 

But I noticed this also.  When Maple hangs, (and it always hangs at least once during this loop), I then click on the button "interrupt the current operation". This does stop the hangs.

Next I do a restart and starts the loop from the loop counter where it hanged in order to continue.  

But It still hangs at that same iteration. I repeate this again, and it still hangs.

Now I close Maple altogether, start Maple again, open same worksheet, and repeat from the same iteration again from where it was at before, now it does not hang.

This tells me that restart and "interrupt the current operation" do not clean everything as expected. Else why only restarting Maple makes it work?

It means mserver.exe (separate process from the frontend) still is caching something related, and that is why it hangs at that iteration.

I can reproduce this each time I run the whole loop from the start.

I can't make a minimal example, since I have no idea where it hangs and why. And it is related to running a long loop.

I just know it hangs when doing odetest() with timeout which never timeout, and it seems random at what iteration it decides to hang.

But my question is really basic here: Does mserver.exe keep any information about the earlier user session/worksheet even after restart ? help says that restarts clear internal memory of the kernel.

Isn't mserver.exe  the Maple kernel? If so, then what could explain that only restarting Maple clears the hang? I am just looking for ideas that could explain this.

This type of problem is the most annoying thing about Maple for me. 

Maple 2020.1 on windows 10.