 original message from jim whitehead ejw cse ucsc edu for toddlers pressing play must cause the music to start immediately within half a second for the toddler to get the causality and not press the button multiple times or some sound indicating that the music will start real soon now as well pressing the button multiple times shouldn t change the semantics like an elevator button no matter how many times you press the elevator still comes to that floor the play button needs to be the same idempotency everywhere you look what would the ideal toddler cd player be like it would immediately start playing a cd after it was loaded it d be an mpNUMBER player with solid state storage instant on 