Build every subgroup of the alternating group on 5 symbols, A5, and check that each is not a normal subgroup (except for the two trivial cases). This command might take a couple seconds to run. Compare this with the time needed to run the .is\_simple() method and realize that there is a significant amount of theory and cleverness brought to bear in speeding up commands like this. (It is possible that your Sage installation lacks GAP's ``Table of Marks'' library and you will be unable to compute the list of subgroups.)