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The Equals and NotEqual operators return true if both names refer to the same tile.
Equals can be abbreviated = and NotEqual can be abbreviated #.

Try the following on the All Here Revisited world:
Forall x (Square(x) and Large(x) -> x=a)
Exists y (Westof(y,a) and y=e)
Exists y (Samerow(y,c) and y#f)

Here is a way to test if at least one but not all tiles have a given property, in this case the property of being a square:

Exists x Square(x) and not Forall x Square(x)

It returns true on the world All Here and false on the world Four Squares.

Precedence and Ambiguity