PRPR 2 (Time-Span Segmentation)
 Let ek the prolongationally most important event in a
 prolongational region (ei-ej). If there is a time-span 
 that contains ei and ek but not ej, prefer a prolonga-
 tional reduction in which ek is an elaboration of ej; 
 similarly with the roles of ei and ej reversed.

 PRPR 3 (Prolongational Connection)
 In choosing the prolongationally most important event 
 in a prolongational region (ei-ej), prefer an ek that 
 attaches so as to form a maximally stable prolon-
 gational connection with one of the endpoints of the 
 region.

 Stability Conditions for Prolongational Connection
 1. (Branching condition)
  a. Right strong prolongations are more stable 
    than right weak prolongations, which in turn are 
    more stable than right progressions.
  b. Left progressions are more stable than left 
    weak prolongations, which in turn are more 
    stable than left strong prolongations.
 2. (Pitch-collection condition) *
 A connection between two events is more stable if 
 they involve or imply a common diatonic collection.
 3. (Melodic condition)
  a. (Distance) A connection between two events is 
    melodically more stable if the interval between 
    them is smaller (with the exception of the oc-
    tave, which is relatively stable).
  b. (Direction) An ascending melodic progression 
    is most stable as a right-branching structure; a 
    descending one is most stable as a left-bran-
    ching structure.
 4. (Harmonic condition) *
  a. (Distance) A connection between two events is 
    harmonically more stable if their roots are 
    closer on the circle of fifths.
  b. (Direction) A progression that ascends along 
    the circle of fifths is most stable as a right-
    branching structure; one that descends along 
    the circle of fifths or produces a subdominant-
    to-dominant-relationship is most stable as a 
    left-branching structure.

 Interaction Principle
 In order to make a sufficiently stable prolongational 
 connection, ek must be chosen from the events in the 
 two most important levels of time span reduction 
 represented in (ei-ej).