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diff --git a/lib/declarative_policy/step.rb b/lib/declarative_policy/step.rb
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+++ b/lib/declarative_policy/step.rb
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+module DeclarativePolicy
+  # This object represents one step in the runtime decision of whether
+  # an ability is allowed. It contains a Rule and a context (instance
+  # of DeclarativePolicy::Base), which contains the user, the subject,
+  # and the cache. It also contains an "action", which is the symbol
+  # :prevent or :enable.
+  class Step
+    attr_reader :context, :rule, :action
+    def initialize(context, rule, action)
+      @context = context
+      @rule = rule
+      @action = action
+    end
+
+    # In the flattening process, duplicate steps may be generated in the
+    # same rule. This allows us to eliminate those (see Runner#steps_by_score
+    # and note its use of a Set)
+    def ==(other)
+      @context == other.context && @rule == other.rule && @action == other.action
+    end
+
+    # In the runner, steps are sorted dynamically by score, so that
+    # we are sure to compute them in close to the optimal order.
+    #
+    # See also Rule#score, ManifestCondition#score, and Runner#steps_by_score.
+    def score
+      # we slightly prefer the preventative actions
+      # since they are more likely to short-circuit
+      case @action
+      when :prevent
+        @rule.score(@context) * (7.0 / 8)
+      when :enable
+        @rule.score(@context)
+      end
+    end
+
+    def with_action(action)
+      Step.new(@context, @rule, action)
+    end
+
+    def enable?
+      @action == :enable
+    end
+
+    def prevent?
+      @action == :prevent
+    end
+
+    # This rather complex method allows us to split rules into parts so that
+    # they can be sorted independently for better optimization
+    def flattened(roots)
+      case @rule
+      when Rule::Or
+        # A single `Or` step is the same as each of its elements as separate steps
+        @rule.rules.flat_map { |r| Step.new(@context, r, @action).flattened(roots) }
+      when Rule::Ability
+        # This looks like a weird micro-optimization but it buys us quite a lot
+        # in some cases. If we depend on an Ability (i.e. a `can?(...)` rule),
+        # and that ability *only* has :enable actions (modulo some actions that
+        # we already have taken care of), then its rules can be safely inlined.
+        steps = @context.runner(@rule.ability).steps.reject { |s| roots.include?(s) }
+
+        if steps.all?(&:enable?)
+          # in the case that we are a :prevent step, each inlined step becomes
+          # an independent :prevent, even though it was an :enable in its initial
+          # context.
+          steps.map! { |s| s.with_action(:prevent) } if prevent?
+
+          steps.flat_map { |s| s.flattened(roots) }
+        else
+          [self]
+        end
+      else
+        [self]
+      end
+    end
+
+    def pass?
+      @rule.pass?(@context)
+    end
+
+    def repr
+      "#{@action} when #{@rule.repr} (#{@context.repr})"
+    end
+  end
+end