i have a problem in using command "collect". 

what should i do ? i face this message when i want to solve my equations? can anyone help me ?view the worksheet

how should i plot from the results of the desolve? i know i should use output=listprocedure,but i do not know how to use it. thank u,
i also have another question? what is the problem with my equations that have singularity ? i used maxfun=0 and stiff=true, but it does not make changes? should i change the initial conditons?maple.mws 

i have a conditional expression like this 

for i from ... do

if .... then
exp1:
exp2:
exp3:
....... 

else 

exp4:
exp5:
exp6:
.... 

end if;

od;

i face this error during caculation:
Error, reserved word `else` unexpected

what should i do?

> with(PDEtools):
> declare(y(x), prime=x):
> ode := diff(diff(y(x),x),x)*diff(y(x),x)*y(x)*f(x)-2*diff(y(x),x)^3*x^6> + 2*diff(y(x),x)^2*y(x)*diff(g(x),x) + y(x)^5; 
 diff(ode,diff(y(x),x));
Error, invalid input: diff received diff(y(x),x), which is not valid for its 2nd argument

 i want to make deravatition with respect to the first deravatives,what should i do?