generate sample space

n=
r=

letters
digits

 option
,'s 
nPr
nCr
words
Powset
Binomial Coeff

second space 
Plus
Minus
Times

r=

nPr
nCr
words
Powset
Binomial Coeff

advanced functions 
P(X) =
regex to exclude
regex to include
starts with 3 or ends with 4 or 5: (^34$5$)

