Optimization constraints

Hello every body, I'm trying to optimize a bunch of parameters (a1,,,,a21). During the optimization, there must be some constraints on these parameters and I have only two: 19.9>= a13 - a20 =>0.1 and 59.9>= a14 - a21 =>0.1 I tried to setup these parameters in comsol (See th image please) but it seems it didn't work properly and therefore I had some errors during the optimization. How to setup these parameters correctly? Any help would be appreciated