36 ;;Quote: a balloon type explicitly restricts sharing state between types; it helps with reasoning about programs

38 ;;Quote: objects of a balloon type can not share internal state with other objects; e.g., primitive data types such as integers and booleans

40 ;;Quote: a balloon type has only one static reference, the reference is external, and no external reference to an internal object

41 ;;Quote: state variables can not store a reference to a pre-existing balloon object; variables and parameters can store references

42 ;;Quote: state variables can only store references to newly created balloon objects; uses deep-copy

45 ;;Quote: balloon type checking verifies that only one external reference exists; e.g., free clusters may be captured by only one balloon and captured clusters can not merge

48 ;;Quote: an opaque balloon type does not expose references to its internal state; internal state can not change between invocations

48 ;;Quote: balloon types are value types if only one reference exists and the type is opaque