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14
4a1s/MFES/PL - Aula 4.md
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@ -29,27 +29,31 @@ pred inv1 {
all x,y : User, z: Photo | x->z in posts and y->z in posts implies x=y
// or (equivalent to 2nd formula)
all x,y : User, z: Photo | x in posts z and y in posts z implies x=y
all x,y : User, z: Photo | x in posts: z and y in posts: z implies x=y
// or (equivalent to 1st and 2nd formula)
all y: Photo | some posts y
all y: Photo | lone posts y
all y: Photo | some posts: y
all y: Photo | lone posts: y
// or (equivalent to 1st and 2nd formula)
all y:Photo | one posts y
all y:Photo | one posts: y
}
pred inv2 {
// Users cannot follow themselves.
all x: User | x->x not in follows
//or
all x: User | x not in x:follows
}
pred inv3 {
// Users can see ads posted by everyone,
// but only see non ads posted by followed users.
all x : User, y :Photo | x->y sees implies (y in Ad) or
(all z:User | z->y in posts implies x->z in follows)
}