@Carl Love 

It works fine, thanks to you.

@Carl Love 

I tried this :

> restart;
> with(Statistics): with(plots):
> P := lambda->RandomVariable(Poisson(lambda)):
> B:=(n,p)->RandomVariable(Binomial(n,p)):
> fish:=pointplot({seq([k,ProbabilityFunction(P(4),k)],k=0..15)},symbol=solidcircle,symbolsize=15,color=red):
> A:=([seq(DensityPlot(B(n,4/n),range=0..n,title=n), n= 10 .. 100,10)],view=[0..15,0..0.25], insequence = true):
> display([fish,A]);

but it gave that error :

Error, (in plots:-display) expecting plot structures but received: [[PLOT(CURVES([[0., 0.], [0., .6046617600e-2]],COLOUR(HSV,.5476190475,1.000000000,.7000000000),THICKNESS(3)),CURVES([[1., 0.], [1., .4031078400e-1]],COLOUR(HSV,.5476190475,1.000000000,.7000000000),THICKNESS(3)),CURVES([[2., 0.], [2., .1209323520]],COLOUR(HSV,.5476190475,1.000000000,.7000000000),THICKNESS(3)),CUR...

In the following program,the last line creates an animate DensityPlot (thanks to the ones who helped me to create it). How can I add the pointplot named "fish" as a fix background to this animation ?

> restart;
> with(Statistics): with(plots):
> P := lambda->RandomVariable(Poisson(lambda)):
> B:=(n,p)->RandomVariable(Binomial(n,p)):
> fish:=pointplot({seq([k,ProbabilityFunction(P(4),k)],k=0..15)},symbol=solidcircle,symbolsize=15,color=red):
> display(fish);
> display([seq(DensityPlot(B(n,4/n),range=0..n,title=n), n= 10 .. 100,10)],view=[0..15,0..0.25], insequence = true);