def duplicates_has(txt: str) -> str:
    seen = ""
    for char in txt:
        if char in seen:
            return char
        seen += char
    return None

def main_6ex():
    txt1 = "banana"
    result = duplicates_has(txt1)
    if result:
        print(f'In {txt1} {result} appears more than once')
    else:
        print(f'In {txt1} no character appears more than once')

    txt2 = "pear"
    result = duplicates_has(txt2)
    if result:
        print(f'In {txt2} {result} appears more than once')
    else:
        print(f'In {txt2} no character appears more than once')

main_6ex()