Solving numerically a multiple integral

savecancel

var("r1, r2, v1, v2")
tau(r1,r2,v1,v2)=((r1-r2)-0.8)/(v1-v2)
E(r1,r2,v1,v2)= exp(-tau(r1,r2,v1,v2)/3)*1.5/tau(r1,r2,v1,v2)^2
f(r1,r2,v1,v2)=exp(-(v1^2+v2^2)/2)*exp(-E(r1,r2,v1,v2)/2)

integral(integral(integral(integral(f(r1,r2,v1,v2),r1,0,10),r2,0,10),v1,-inf,inf),v2,-inf,inf)

RuntimeError: ECL says: In function GCD, the value of the second argument is 1.0 which is not of the expected type INTEGER

Could anyone help me please?