text: Depending on the vehemence of the technique, Hovhaness's published scores annotate these sections variously, for example as "Free tempo / humming effect" and "Repeat and repeat ad lib, but not together".In Europe, following the introduction of the expression "aleatory music" by Meyer-Eppler, the French composer Pierre Boulez was largely responsible for popularizing the term. Other early European examples of aleatory music include Klavierstück XI (1956) by Karlheinz Stockhausen, which features 19 elements to be performed in a sequence to be determined in each case by the performer. A form of limited aleatory was used by Witold Lutosławski (beginning with Jeux Vénitiens in 1960–61), where extensive passages of pitches and rhythms are fully specified, but the rhythmic coordination of parts within the ensemble is subject to an element of chance. There has been much confusion of the terms aleatory and indeterminate/chance music. One of Cage's pieces, HPSCHD, itself composed using chance procedures, uses music from Mozart's Musikalisches Würfelspiel, referred to above, as well as original music. Types of indeterminate music
  Some writers do not make a distinction between aleatory, chance, and indeterminacy in music, and use the terms interchangeably. 