Hello!

I'm wondering can this problem be simply solved by mathematica?

I'd like to plot a region of function
F(x,y,a,b)<1, {x,0,1}, {y,0,1}
but also for parameters {a,0,1} {b,0,1}

saying it in a better way,
a sum of regions F(x,y,a,b)<1, {x,0,1}, {y,0,1} for {a,0,1} {b,0,1}

Do you have a clue?