How “there is” (∃) works

∃x needs one witness: a single piece that makes the rest true.

T∃x Tet(x)

One tetrahedron is enough. It is the witness.

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How it works

∃x (Cube(x) ∧ Small(x)) reads “there is a piece x that is a cube and is small.” Point at one small cube and you are done.

Pair ∃ with ∧. With → instead, the sentence turns true as soon as anything is not a cube, which is almost never what you mean.

0 of 5 right

Question 1

∃x (Cube(x)∧Large(x))

Question 2

∃x (Tet(x)∧Small(x))

Question 3

∃x Dodec(x)

Question 4

∃x (Large(x)∧FrontOf(x, a))

Question 5

∃x (Cube(x)∧Adjoins(x, a))