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NOT.4:3 - Forces
| Force | What must be reconciled |
|---|
| Easier use and retained distinctions | A compact or regular expression can discard information needed by another operation. |
| Local manipulation and surrounding context | Replacing a part must respect the names, connections and assumptions supplied by its surroundings. |
| One useful result and a reusable rule | A successful instance supports that instance; a rule for a family needs an argument covering that family. |
| More alternatives and search cost | Keeping several equivalent forms can enable a later move while increasing the work of finding and comparing them. |
| Meaning and execution | Equal mathematical values can come from computations or actions with different effects and costs. |