Forty-seven symbols of written mathematics fall into six families: relations, logic, sets, number systems, operations and calculus. The number systems nest, ℕ ⊂ ℤ ⊂ ℚ ⊂ ℝ ⊂ ℂ, and ∅ is a subset of every set. n! counts the orderings of n objects and ⁿCᵣ = n!/(r!(n −