findall/3 is a special case of bagof/3, where all free
variables in the generator are taken to be existentially quantified.
Thus the use of the operator ^ is avoided. Because
findall/3 avoids the relatively expensive variable analysis done
by bagof/3, using findall/3 where appropriate rather than
bagof/3 can be considerably more efficient.
findall/4 is a variant of findall/3 with an extra argument
to which the list of solutions is appended. This can reduce the amount
of append operations in the program.