Inv (function prefix)
In mathematics, the inverse function of a function f (also called the inverse of f) is a function that undoes the operation of f. The inverse of f exists if and only if f is bijective, and if it exists, is denoted by 
  
    
      
        
          f
          
            −
            1
          
        
        . {\displaystyle f^{-1}.} For a function 
  
    
      
        f
        :
        X
        →
        Y
      
    
    {\displaystyle f\colon X\to Y}
  
, its inverse 
  
    
      
        
          f
          
            −
            1
          
        
        :
        Y
        →
        X
      
    
    {\displaystyle f^{-1}\colon Y\to X}
  
 admits an explicit description:  it sends each element 
  
    
      
        y
        ∈
        Y
      
    
    {\displaystyle y\in Y}
  
 to the unique element 
  
    
      
        x
        ∈
        X
      
    
    {\displaystyle x\in X}
  
 such that f(x) = y. As an example, consider the real-valued function of a real variable given by f(x) = 5x − 7. One can think of f as the function which multiplies its input by 5 then subtracts 7 from the result.