The following is a list of 15 thought provoking statements
about sets where a true or false answer is needed.
A denotes any set, F the set {1,2}, φ the empty set,
and ℘(S) the set of all subsets of set S (i.e, the power
set of S).

a) φ∩{φ} = {φ}
b) φ∪{φ} = {φ,{φ}}
c) φ ∈ ℘({φ,{φ}})
d) {φ} ⊆ A
e) φ ⊆ A
f) φ ⊆ ℘(A)
g) {{φ}} ⊆ ℘(φ)
h) {φ}∩φ = φ
i) ℘(φ) = {φ,{φ}}
j) φ ∈ A
k) φ ∈ ℘(A)
l) {φ} ∈ ℘(A)
m) {φ}∪φ = {φ}
n) φ ⊆ ℘(F)-φ
o) {φ} ⊆ {{φ,{φ},{{φ}}}}

From "Bridge to Abstract Mathematics",1987
by Ronald P. Morash.