<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def unique(seq):
 """Helper function to include only unique monomials in a basis."""

    seen = {}
    result = []
    for item in seq:
        marker = item
        if marker in seen:
            continue
        seen[marker] = 1
        result.append(item)
    return result