<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def expr_contains(e, o):
    ''' Returns true if o is in e '''
    if o == e:
        return True
    if e.has_args():
        for a in e.args():
            if expr_contains(a, o):
                return True
    return False