The entries of the internal list are either digits (0-x) or expressions. To ensure a valid mapping of these values to an input vector (as done when an optimizer provides input parameters), we have to linearize the list (done whenever modifying the list, see the different flex_* functions )
linearize_internal_list(internal_list)another list, but with remapped digits in increasing order, while leaving expressions or digits of 0 untouched.
the internal list, with entries for each parameter x condition combination
flex_vary_prms(), flex_restrain_prms(),
flex_fix_prms(), flex_special_dependency()