FCAntiSymmetrize[expr, {a1, a2, ...}] antisymmetrizes expr with respect to the variables a1, a2, ....
FCAntiSymmetrize[f[a, b], {a, b}]\frac{1}{2} (f(a,b)-f(b,a))
FCAntiSymmetrize[f[x, y, z], {x, y, z}]\frac{1}{6} (f(x,y,z)-f(x,z,y)-f(y,x,z)+f(y,z,x)+f(z,x,y)-f(z,y,x))