Final answer:
The notation 'fun x y -> e' is used in functional programming to define anonymous functions that take multiple arguments, where 'fun' introduces the function, 'x' and 'y' are the parameters, and 'e' is the expression forming the body of the function.
Step-by-step explanation:
The expression fun x y -> e is a form of syntactic sugar found in functional programming languages. This succinct notation is used to define anonymous functions, or lambdas, that take multiple arguments. The fun keyword starts the declaration, followed by the arguments x and y.
The arrow -> separates the function's parameters from its body, represented here by e, which is an expression that becomes the function's return value when applied to its arguments. In a more verbose syntax, this could be written as function(x) { return function(y) { return e; }; }, where each function only takes one argument, because some functional programming languages always curry functions. It emphasizes the idea that every function actually takes a single argument and returns a function that takes the next argument, repeating this process until all arguments are taken.