class Steep::Subtyping::Constraints

def to_s
  strings = each.map do |var, lower_bound, upper_bound|
    "#{lower_bound} <: #{var} <: #{upper_bound}"
  end
  "#{unknowns.to_a.join(",")}/#{vars.to_a.join(",")} |- { #{strings.join(", ")} }"
end