a subclass of Expression; represents the result of a well-defined mathematical operation or character manipulation on two Expression operands, which are distinguished. Instances of this class are distinct operations, such as integer-addition, real-addition, set-union, string-compare-equal, etc.

represents the operand Expression that produces one input to a BinaryOperation, distinguished (if needed) as the "left" operand in the definition of the operation

represents the operand Expression that produces one input to a BinaryOperation, distinguished (if needed) as the "right" operand in the definition of the operation.