deferred class GROUP_ELEMENT General cluster: time description: "Invertible object with an internal + operation. Note: The model is that of a commutative group." Ancestors ANY Queries infix "+" (other: [like Current] GROUP_ELEMENT): [like Current] GROUP_ELEMENT infix "-" (other: [like Current] GROUP_ELEMENT): [like Current] GROUP_ELEMENT prefix "+": [like Current] GROUP_ELEMENT prefix "-": [like Current] GROUP_ELEMENT zero: [like Current] GROUP_ELEMENT Constraints neutral addition self subtraction