set of allowed input values
set of all possible output values of the function
set of output types
maps different inputs to different outputs
if it covers the entire output set (in other words, if the image of the function is equal to the function’s codomain).
if it is both injective and surjective. In this case, f is a one-to-one correspondence between the input set and the output set: for each of the possible outputs y ∈ Y (surjective part), there exists exa