In a function, you feed in x and get y.
In the inverse function, if you feed in y, you get x
So basically if you take the inverse of the original function, you get back the original input.
Hence:
H^-1(H(x)) = x
Take this example:
H(x) = 3x
H^-1(x) = x/3
H^-1(H(7))
--> H(7) = 3(7) = 21
--> H^-1(21) = 21/3 = 7
