There is difference between functions and expressions: programming language functions produce values, expressions are values which represent symbolic information. In the past max was ordinary function. max used order on expression to pick "bigger" argument, quite unlike expected symbolic behaviour. Now in FriCAS expressions are no longer ordered and old max definition does not work, freeing the name so that we can give it symbolic meaning.

    functions with signatures like (a,b,B(a))->(C(a,b))

    Odd(0)=false, Odd(n)=Even(n-1)
    Even(0)=true, Even(n)=Odd(n-1)