Discover two integers such that at the very least one exists in every given Pair

def examine(x, y, arr, n):

    for i in vary(1, n):

        if arr[i][0] == y or arr[i][1] == y

                or arr[i][0] == x or arr[i][1] == x:

            proceed

        else:

            return True

    return False

def findIndex(x, arr, n):

    for i in vary(1, n):

        if arr[i][0] != x and arr[i][1] != x:

            return i

    return n

def discover(a, n):

    x = a[0][0]

    ok = findIndex(x, a, n)

    if ok >= n:

        return 'YES'

    y = a[k][0]

    flag = 0

    if examine(x, y, a, n):

        y = a[k][1]

        if examine(x, y, a, n):

            x = a[0][1]

            ok = findIndex(x, a, n)

            if ok >= n:

                return 'YES'

            y = a[k][0]

            if examine(x, y, a, n):

                y = a[k][1]

                if examine(x, y, a, n):

                    return 'NO'

    return 'YES'

if __name__ == '__main__':

    N = 6

    M = 5

    arr = [[2, 3], [2, 4], [2, 5], [3, 4], [3, 5], [4, 5]]

    print(discover(arr, N))