Logic

• How to Prove (∀x P(x) → A) → ∃x(P(x) → A)
  A classical proof uses cases on A and requires a nonempty domain; the statement is not generally valid in intuitionistic logic.
• How Much Did the Shop Lose in the Stolen-Money Riddle?
  In the classic stolen-money riddle, the shop loses $100 at selling price: $70 in goods and $30 in change, not $200.