Upside-down intersection signs

[pedro353]

On page 6: "The intersection of two sets A and B, denoted A∪B, is the set of all elements x such that[...]"
On equation 0.1.4: A ∪ B = {x | x ∈ A ∧ x ∈ B}
On example 0.1.1: "The intersection of the sets A = {1,2,3,4} and B = {3,4,5,6} is the set A∪B = {3,4}.
The intersection of the sets C = {0,1,2,6,7} and D = {3,9,−4,5} is the empty set ∅"

The intersection signs are upside down.