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#### 2.7.8.2 Fan

In cases where a deconstructions would be needed to apply the same function to both sides of a pair, the overhead can be avoided by means of a property of the virtual machine intended for that purpose.

A `silly` definition of `fan` implying the following theorem is helpful in expressing such an application.

T14

  [[`fan`]] `f` = `((nil,nil),((nil,f),(nil,nil)))`

The virtual machine recognizes when an application has the form shown above, and uses `f` as a function to be applied to both sides of the argument.

P13

  ([[`fan`]] `f`) `(x,y)` = `(f x,f y)`

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