How do you map b into a to get [[a1,a2,b1],[a3,a4,b2],[a5,a6,b3]]

a:=[[a1,a2],[a3,a4],[a5,a6]]
b:=[b1,b2,b3]

How do I keep Maple from changing the variable xi to the greek letter?

The help page mentions that filledregions=true, that regions defined by curves are filled with different colors

implicitplot({y = x^2, y = x+5}, x = -10 .. 10, y = -10 .. 10, numpoints = 5000, filledregions = true)

What I expected was that the region between the line and the curve would be a different colored region.

As an example, how can I overlap the timing of these two pointplots in the same plot?

with(plots);
a := animate(pointplot, [[[3, 2], [2, 5], [5, 2], [5, 5]], transparency = A], A = 0 .. 1);
b := animate(pointplot, [[[2, 2], [4, 5], [3, 2], [3, 3]], transparency = A], A = 0 .. 1);
display(a, b, insequence = true, view = [0 .. 10, 0 .. 10]);

I want the second plot to appear 2 seconds later as the first plot is still fading away. 

I have a loop that will map specific locations of a set of lists into a new set of lists.

Suppose
a1:=[1,2,3,4,5,6,7]
a2:=[9,8,7,6,5,4,3]
a3:=[4,5,4,5,4,5,4]
:
etc ...

for i from 1 to 3 do
  b||i:=map(a||i->a||i[4],a||i[6],a||i):  #map positions 4 and 6 from a into b
end do:

I get Error, invalid parameters for inline function.