Question: Numerical integration


I´m Trying to do numerical integration for a function defined by a product of characteristic functions. I either receive the message " Error, (in unknown) too many levels of recursion " or "error, (in evalf/int) unable to handle singularity". What should I do?

f_1:=(x,y,z,w)->piecewise(x+w > 0 , 1);
f_2:=(x,y,z,w)->piecewise(x*w - y*z > 0,1);
f_3:=(x,y,z,w)->piecewise((x+w)^2 - 4*(x*w - y*z)<0,1);

I want to integrate prod, with all four variables ranging from -1 to 1.

Thank you, Bernardo

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