What is the name for a pair of functions fulfilling f∘g=g, g∘f=f?
If I have an unknown function ƒ(a,b), such that ƒ(1,1) =1; ƒ(2,1) =2; ƒ(3,1) =2.5; ƒ(4,1) =3; ƒ(5,1) =3.5; and so on, what's my equation?