Answer these questions for the poset ({{1}, {2}, {4}, {1, 2}, {1, 4}, {2, 4}, {3, 4}, {1, 3, 4}, {2, 3, 4}}, ⊆).
a) Find the maximal elements.
b) Find the minimal elements.
c) Is there a greatest element?
d) Is there a least element?
e) Find all upper bounds of {{2}, {4}}.
f) Find the least upper bound of {{2}, {4}}, if it exists.
g) Find all lower bounds of {{1, 3, 4}, {2, 3, 4}}.
h) Find the greatest lower bound of {{1, 3, 4}, {2, 3, 4}}, if it exists.