Redundancy in simple terms is more information than needed or duplicate information, etc. Redundancy does not have to contradict the minimum information principle and may even be welcome. The problem of redundancy is too wide for this short text. Here are some examples that are only to illustrate that minimum information principle cannot be understood as minimum number of characters or bits in your collections or even items:

• passive and active approach: if you learn a foreign language, e.g. Esperanto, you will often build word pairs such as phone-telefono, language-lingvo, hope-esperanto, etc. These pairs require active recall of the foreign word. Active recall does not, however, guarantee passive recognition and you may fail with telefono-phone, lingvo-language, or esperanto-hope. Adding new elements with swapped questions and answers may in some cases be redundant but it does not contradict the minimum information principle! Your items are still as simple as possible. You just get more of them
  In SuperMemo 2000/2002, you can quickly generate swapped word-pair items with Duplicate (Ctrl+Alt+D) and Swap (Ctrl+Shift+S)
• reasoning cues: you will often want to boost your reasoning ability by asking about a solution to the problem. Instead of just memorizing the answer you would like to quickly follow the reasoning steps (e.g. solve a simple mathematical equation) and generate the answer. In such a case, providing the hint on the reasoning steps in the answer will only serve helping you always follow the right path at repetitions
• derivation steps: in more complex problems to solve, memorizing individual derivation steps is always highly recommended (e.g. solving complex mathematical problems). It is not cramming! It is making sure that the brain can always follow the fastest path while solving the problem. For more on boosting creativity and intelligence read: Roots of genius and creativity, as well as more specific: Derivation, reasoning and intelligence
• multiple semantic representation: very often the same knowledge can be represented and viewed from different angles. Memorizing different representations of the same fact or rule is recommended in cases where a given memory is of high value. This will increase the expected recall rate (beyond that specified with the forgetting index)!
• flexible repetition: if there are many valid responses to the same question make sure that your representation makes it possible to identify the equivalence and reward you with good grades by providing just one of the equivalent choices. For example, if you learn a language, it rarely make sense to learn all synonyms that meet a definition of a concept. It is more adequate to consider a single synonym as the sufficient answer (e.g. a mark made by ink spilt on sth = blot/blob/blotch)