User blog comment:Alemagno12/The Addition and Substraction functions./@comment-25337554-20151230055624/@comment-27173506-20151230163847

The whole point is that the X function does not support a-b. If I wanted to redefine your two functions, here is how I would do it:

A(0,x)=x

A(Sx,y)=A(x,Sy)

The Sn=n+1 operation is allowed

B(x,0)=x

B(Sx,Sy)=B(x,y)

This doesn't use the - symbol and uses less symbols.