ex9.rb

minus = -> f,g { -> x { f.(x) - g.(x) } } # f - g 
div = -> f,g { -> x { f.(x) / g.(x) } } # f / g 
mult = -> f,g { -> x { f.(x) * g.(x) } } # f * g 
norm = -> f { -> x { f.(x).abs}} # absolute value 
const = -> const { -> x { const} } # That's right, the constant function !  

# You should recognize these: 
plus_eps = -> eps { -> f { -> x { f.(x+eps) } } } 
min_eps = -> eps { -> f { -> x { f.(x-eps) } } }  

# is f < g ?  
inf = -> f,g { -> x { f.(x) < g.(x) } }