Task: Sentence Ordering
Input (English): Steps: (1) A star burns in space (2) Eventually it burns all its hydrogen (3) Becomes a red giant (4) Once the red giant burns itself out (5) The core of the star collapses (6) The gasses will start to disperse (7) A white dwarf has been formed.  
Where does the following step fit into the given list of steps: Only the core is left 
Output (English):  After step 6.