sheffer.swift

infix operator |: MultiplicationPrecedence
infix operator ∧: MultiplicationPrecedence
infix operator ∨: MultiplicationPrecedence
infix operator ⊃: MultiplicationPrecedence
prefix operator ¬

func |(lhs: Bool, rhs: Bool) -> Bool {
    switch (lhs, rhs) {
    case (true, true): return false
    case (true, false): return true
    case (false, true): return true
    case (false, false): return true
    }
}

prefix func ¬(value: Bool) -> Bool {
    return value | value
}

func ∧(lhs: Bool, rhs: Bool) -> Bool {
    return (lhs | rhs) | (lhs | rhs)
}

func ∨(lhs: Bool, rhs: Bool) -> Bool {
    return (lhs | lhs) | (rhs | rhs)
}

func ⊃(lhs: Bool, rhs: Bool) -> Bool {
    return lhs | (rhs|rhs)
}