define constants inside a laplace function

I'd like to get the Laplace of a window function. I'd get the right output if I write this:

b=1;a=2;
syms t s
laplace((heaviside(t-a)-heaviside(t-b)))

ans =

exp(-2*s)/s - exp(-s)/s

but I'd like to preserve a and b as constants. However when I defined as " syms t s a b " it doesn't give the Laplace Transform because there's too many variables. Thanks!

Answer 1

[Walter Roberson]

laplace((heaviside(t-a)-heaviside(t-b)), t, s)