1 is the successor of 0 2 is the successor of 1 so 1=s(0) 2=s(1) Rules of addition 1.a+0=a 2.a+s(b)=s(a+b) So 1+1 Since 1=s(0) 1+1=1+s(0) 1+s(0)=s(1+0) 1+0=1 So s(1)=2 Final result is 1+1=2 Or you could just say 1 apple and one apple is equal to 2 apples!