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- A unary function
`f`defines a binary relation (the*function graph*):`S`:= {<`x`,`y`>:`y`=`f`(`x`)}. - A binary relation
`S`defines a function, if the first component of every tuple in`S`is unique:`f`(`x`) :=**such**`y`: <`x`,`y`> in`S`.

*We may interpret a special binary relation as a unary function.*

Author: Wolfgang Schreiner

Last Modification: October 14, 1999