Nonretrogradable Rhythms

Nonretrogradable rhythms (also, non-retrogradable or palindromic rhythms) correspond to sequences of note-durations arranged symmetrically, resulting in rhythmic sequences that remain identical when played forwards and backwards, that is,  reversing the order of an object's contents leaves the original object unaltered. It is common to find nonretrogradable rhythms that are designed around one central duration value serving as axis of symmetry.