∀ {f : Aesop.Frontend.Feature} {children : Array Aesop.Frontend.RuleExpr} {f_1 : Aesop.Frontend.Feature}
  {children_1 : Array Aesop.Frontend.RuleExpr},
  Aesop.Frontend.RuleExpr.node f children = Aesop.Frontend.RuleExpr.node f_1 children_1 →
    f = f_1 ∧ children = children_1