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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _convert_nominal_form( analysis ):
    ''' Converts nominal categories of the input analysis. 
        Performs one-to-one conversions only. '''
    assert FORM in analysis, '(!) The input analysis does not contain "'+FORM+'" key.'
    for idx, pattern_items in enumerate(_noun_conversion_rules):
        pattern_str, replacement = pattern_items
        if pattern_str in analysis[FORM]:
           analysis[FORM] = analysis[FORM].replace( pattern_str, replacement )
    return analysis