def f(*args):
    result = []
    for x in args[0]: 
        if x in result: 
            continue 
        for word in args[1:]: 
            if x not in word: 
                break 
        else: 
            result.append(x) 
    return ''.join(result)
s1, s2, s3 = "message", "massage", "mask"
print(f(s1, s2, s3))

def f(*args):
    result = []
    for x in args[0]:  
        for word in args[1:]: 
            if x not in word: 
                break 
        else: 
            result.append(x) 
    return ''.join(result)
s1, s2, s3= "message", "massage", "mask"
print(f(s1, s2, s3))

def f(*args):
    res = ""
    l = len("".join(args[:-1]))
    for i, s in enumerate("".join(args)):
        if i > l:
            res += s
    return res
s1, s2, s3= "one", "two", "three"
print(f(s1, s2, s3))

def f(*args):
    result = []
    for seq in args:
        for x in seq:
            if not x in result:
                result.append(x)
    return ''.join(result)
s1, s2, s3 = "message", "massage", "mask"
print(f(s1, s2, s3))

x = [1, 2, 3]
y = sorted(x)
y.insert(0, 100)
print(x[0])

x = [2, 1, 3]
x = x.sort()
print(x[0])

class A:
    pass
class B(A):
    pass
a = A()
b = B()
print(isinstance(b, A), isinstance(a, B))

x = 'str' * 2
y = 'str' * 2.0
print(x == y,  x is y)