def successive (a) :
    a=a+1
    return a 
assert successive(2)==3
res = successive(2)
print(res)

def predecesseur (b):
    if b>0:
        p = b-1
        return p 
    else:
        return None 
assert predecesseur(3) == 2
assert predecesseur(0) == None 
res = predecesseur(3)
print(res)

def addition(a,b):
    while a>0:
        a=predecesseur(a)
        b=successive(b)
    return a+b
res = addition(2,3)
print(res)

def multiplication(a,b):
    c=0
    while a>0:
        c=c+b
        a=predecesseur(a)
    return c 
res = multiplication(2,3)
print(res)