contraposition
contrapositionnoun- [mass noun](Logic)conversion of a proposition from all A is B to all not-B is not-A
(逻)换质位法(如将命题all A is B 换成all not-B is not-A)
派生contrapositive( & ) adjective& noun语源- mid 16th cent.: from late Latin contrapositio(n-), from the verb contraponere, from contra- 'against' + ponere 'to place'
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