Add a more detailed explanation.

diff --git a/src/sicp/ex3_31.rkt b/src/sicp/ex3_31.rkt
index 4b78357d62230364de4f85ee62b7890effffd5f3..fae2074f3f669529d14ba4a6f543fab0964e0e03 100644 (file)
--- a/src/sicp/ex3_31.rkt
+++ b/src/sicp/ex3_31.rkt
@@ -16,6 +16,10 @@ Let us take half adder example:
     (and-gate d e s)
     'ok))
 
+The gate procedures like inverter and or-gate calls add-action! which
+is the procedure which adds the gate operation to the agenda. If it
+is not called once, then the operation is not added into the agenda.
+
 If accept-action-proc! is defined without the call to proc, i.e.
 
 (define (accept-action-proc! proc)