An aside all about numbers

See notes for:

• Sets and the empty set ∅ or { }
• Roster notation { 5, 6, 3, 1}
• Positive integers { 1, 2, 3, 4, ... } and non-negative integers (ℕ) { 0, 1, 2, 3, 4, ... }
• Set-builder notation {a+b | a and b are positive integers}
• Rational numbers (ℚ) can be express as a fraction integer over positive integer
• Real numbers (ℝ) have a decimal representation
  • All rationals are real