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MATH.20:3 - Forces
| Force | Tension |
|---|
| Obtaining and comparing | It can be easier to bound a result than to construct it, but the comparison still needs an argument. |
| Direction | Feasible constructions and relaxed problems bound optima in different directions. |
| Tightness | A simpler bound can be cheaper; a tighter one matters only through the result it enables. |
| Propagation | An operation can preserve, reverse or destroy a comparison. |
| Attainability | A bound may be approached without being attained, or may require incompatible equality conditions. |
| Reuse | A proved comparison remains useful while its domain and premises survive. |