:=
x := e -- assign the value e to the new local variable x
f X := (x) -> ( ... ) -- install a method for the method function
f acting on an argument of class X.
X * Y := (x,y) -> ( ... ) -- install a method for the operator
* applied to arguments of classes X and Y.
Many other operators are allowed: see operators.
This operator is slightly schizophrenic in its function, as the installation
of a method has global effect if the classes involved are globally known,
as is typically the case, whereas the assignment of a value to a local
variable is never globally known.
