| 21. | First, let be the force of tension as a function of.
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| 22. | Let be a vector subspace of the topological vector space.
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| 23. | Let be a set with a binary operation " on it.
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| 24. | For example, let be the proposition that it is raining outside.
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| 25. | Notational conventions : Let be a variable ranging over sets of sentences.
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| 26. | Let be the corresponding nested sequence of " coordinate " subspaces of.
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| 27. | If is even, then let be an isotropic subspace complementary to.
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| 28. | Let be a semidirect product of the normal subgroup and the subgroup.
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| 29. | Let be a bounded self-adjoint operator on a Hilbert space.
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| 30. | Formally, let be a bipartite graph with parts } and }.
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