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- It is
*wrong*to write

because from 6|12 we cannot conclude f(12) = 6.Let `f`(`x`) be the`y`such that`y`|`x`. - We may define

because we can prove unicity:Let `x`/`y`be the`q`such that`q`*`y`=`x`.

Since 3*4=12, we may thus conclude 12/4 = 3.( **forall**`x`,`y`,`q`:`q`*`y`=`x`=> (**forall**`q`':`q`'*`y`=`x`=>`q`=`q`'))

Author: Wolfgang Schreiner

Last Modification: October 14, 1999