9.1.2 Computing with units
Xcas performs usual arithmetic operations (+, -, *, /,
unit objects. Different units may be used, but they must be
compatible for + and -. The result is an unit object
multiplication and the division of two unit objects
_u1 and _u2 the unit of the result is written
_(u1*u2) or _(u1/u2).
- for an addition or a subtraction of compatible unit objects,
the result is expressed with the same unit as the first term of the operation.