Range

A Range is typically constructed with a range literal:

x..y  # an inclusive range, in mathematics: [x, y]
x...y # an exclusive range, in mathematics: [x, y)

# Example:
0..5.to_a # => [0, 1, 2, 3, 4, 5]
0...5.to_a # => [0, 1, 2, 3, 4]

An easy way to remember which one is inclusive and which one is exclusive it to think of the extra dot as if it pushes y further away, thus leaving it outside of the range.