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Functions as Equations

More convenient form of specification

•  add: (N × N) => N

  add(m,n) = m+n

•  duplicate: R => R ×R, = {1,4,7}

  duplicate(r) = (r,r)

•  which: (B+N) => {isbool,isnum}

  which(m) =

  cases m of

  isB(b) => isbool isN(n) => isnum

  end

•  singleton: N => P(N)

  singleton(n) = {n}

• nothing: B intersect N => B

  no equational definition (domain empty)!

Equations are just function representations!