Here I difine a subfunction:

mandelbrot := proc(x, y)
local c, z, m;
c := evalf(x+y*I);
z := c;
for m to 30 while abs(z) < 2 do
z := z^2+c
od;
abs(z);
end:

Then I want to plot this function using densityplot command:

plots[densityplot](mandelbrot, -2 .. 0.7, -1.2 .. 1.2, grid=[50, 50], style=patchnogrid, scaling=constrained);#This command is right.

But...

plots[densityplot](mandelbrot(x,y), x=-2 .. 0.7, y=-1.2 .. 1.2, grid=[50, 50], style=patchnogrid, scaling=constrained);#Error, the proc I defined could not determine whether abs(x+1.*I*y) < 2.

I know these two integrals: int(sin(x)/x,x=0..infinity)=Pi/2 and int((sin(x)/x)^2,x=0..infinity)=Pi/2, so I want to know the answer to this integral int((sin(x)/x)^n,x=0..infinity), here n is a positive integer. Only assume(n>0) and additionally(n, integer) and then enter the above statement, Maple could not give an answer. Then I want to know whether there is an exact symbolic result of the integral and if so, how can I get it in Maple. 3x...