Model definition - multiple LSF

Hi,
Thanks for the amazing software UQLab. Please I have a major challenge in developing the model for multiple Limit State Functions. Any help will be highly appreciated

For example:

Probability of Failure (System) = Pr { g1(X) > 0 and g2(X)=<0 and g3(X)=<0}
g1(X)=X1-X2
g2(X)=(X1^2)-X3
g3(X)=X2+X3-X4
All variables are standard normal

My challenge is how to set-up the MOpts.mString for the given condition of system failure. If I can understand how this example is set up in uqlab especially given that g1(X)>0; it will go a long way in helping me.

Appreciate your input please.