    class
    	BOOLEAN_REF

    General
    	cluster: base
    	description: "References to objects containing a boolean value"

    Ancestors
    	HASHABLE*

    Queries
    	hash_code: INTEGER_32
    	infix "and then" (other: [like Current] BOOLEAN_REF): BOOLEAN
    	infix "and" (other: [like Current] BOOLEAN_REF): BOOLEAN
    	infix "implies" (other: [like Current] BOOLEAN_REF): BOOLEAN
    	infix "or else" (other: [like Current] BOOLEAN_REF): BOOLEAN
    	infix "or" (other: [like Current] BOOLEAN_REF): BOOLEAN
    	infix "xor" (other: [like Current] BOOLEAN_REF): BOOLEAN
    	is_hashable: BOOLEAN
    	item: BOOLEAN
    	out: STRING_8
    	prefix "not": [like Current] BOOLEAN_REF
    	to_integer: INTEGER_32
    	to_reference: BOOLEAN_REF

    Commands
    	set_item (b: BOOLEAN)

    Constraints
    	involutive negation
    	non contradiction
    	completeness