let help = "set the default level of slicing used to propagate to the calls\n0 : don't slice the called functions\n1 : don't slice the called functions but propagate the marks anyway\n2 : try to use existing slices, create at most one\n3 : most precise slices\nnote: this value (defaults to 2) is not used for calls to undefined functions\nexcept when '-slice-undef-functions' option is set"