:: Built-in Concepts
:: by Andrzej Trybulec
::
:: Received January 1, 1989
:: Copyright (c) 1990 Association of Mizar Users


begin

definition
mode set -> set ;
end;

definition
let x, y be set ;
pred x = y;
reflexivity
errorfrm
;
symmetry
errorfrm
;
end;

notation
let x, y be set ;
antonym x <> y for x = y;
end;

definition
let x, X be set ;
pred x in X;
asymmetry
errorfrm
;
end;