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Logical biconditional
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==Colloquial usage== One unambiguous way of stating a biconditional in plain English is to adopt the form "''b'' if ''a'' and ''a'' if ''b''"βif the standard form "''a'' if and only if ''b''" is not used. Slightly more formally, one could also say that "''b'' implies ''a'' and ''a'' implies ''b''", or "''a'' is necessary and sufficient for ''b''". The plain English "if'" may sometimes be used as a biconditional (especially in the context of a mathematical definition<ref>In fact, such is the style adopted by [[wikipedia:Manual of Style/Mathematics|Wikipedia's manual of style in mathematics]].</ref>). In which case, one must take into consideration the surrounding context when interpreting these words. For example, the statement "I'll buy you a new wallet if you need one" may be interpreted as a biconditional, since the speaker doesn't intend a valid outcome to be buying the wallet whether or not the wallet is needed (as in a conditional). However, "it is cloudy if it is raining" is generally not meant as a biconditional, since it can still be cloudy even if it is not raining.
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