# Universal restriction in description logic

1. Jan 19, 2012

### ferrelhadley

I am struggling to understand how a universal restriction works in description logic. I can understand the extistential restriction but not the universal.

the definition is

I have two examples with answers for this.

For the first one (B AND A) is easy enough to work out: (a,b,d,f)
Now the answer given is (f,e,d) the only way I can ge to (f,e,d) is to look at every x elelment in the relation R and it is (a,b,c) and hence the negation would be (d,e,f). However as hard as I appy (a,b,d,f) I cannot get to (d,e,f).

I have tried using the (a,b,d,f) as the x value in the R relation but that would be only (a,c)
I have tried using it as the y value but that would be (a,c) again nothing like the answer provided.
Anyone have any ideas or am I totally lost here?

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