In a string, how can I find a letter of both upper and lower case?

ie/ something like

StringTools[SearchAll]("h" and "H" , string)

In the Signal Processing Webinar there existed a few worksheets I would like to request,

Ultrasound Transmission through a Band Gap Medium + xls data
Coded Excitation Signal analysis
Acoustic Scattering

If anyone would be so kind to provide these worksheets?

There was mention to have simplify=false in Maple to stop it from it's automatic manipulation which would otherwise be considered obvious but not necessarily wanted. 

The idea brings up numeric manipulation. 

For example how do I force maple to factor out (1/3) from this :

a:= (1/3)*x^2 + (1/6)*x - (1/12)

to to show this

(1/3) * ( x^2 + x/2 - 1/4 )

Things brings up another question, the collect command...

Maybe I'm missing something but I thought boys surface was one surface and when I plot it in maple it appears to have two surfaces.

with(plots):
plot3d(sqrt(25-x^2-y^2),x=-6..6,y=-6..6,axes=box)

Notice it doesn't completely go down to the x-axis. 

It can be partially fixed with this

plot3d(sqrt(25-x^2-y^2),x=-6..6,y=-sqrt(25-x^2)..sqrt(25-x^2),axes=box)

but due to bugs in earlier versions of maple I can only achieve this