diff --git a/lib/lrama/states.rb b/lib/lrama/states.rb
index 0ed4bff9..f56b0e9b 100644
--- a/lib/lrama/states.rb
+++ b/lib/lrama/states.rb
@@ -41,6 +41,8 @@ def initialize(grammar, trace_state: false)
       # value is array of [state.id, nterm.token_id].
       @reads_relation = {}
 
+      # `Read(p, A) =s DR(p, A) ∪ ∪{Read(r, C) | (p, A) reads (r, C)}`
+      #
       # `@read_sets` is a hash whose
       # key is [state.id, nterm.token_id],
       # value is bitmap of term.
@@ -62,6 +64,8 @@ def initialize(grammar, trace_state: false)
       # value is array of [state.id, nterm.token_id].
       @lookback_relation = {}
 
+      # `Follow(p, A) =s Read(p, A) ∪ ∪{Follow(p', B) | (p, A) includes (p', B)}`
+      #
       # `@follow_sets` is a hash whose
       # key is [state.id, rule.id],
       # value is bitmap of term.