REM Goal loop example
REM =================
REM This knowledge base will produce run time error 205 (Goal loop)
REM The first rule tried will be [loop 2] because it can determine a value of the [action] attribute.
REM The backward chaining process tries to find rules to conclude goals an interim goals before invoking a prompt
REM A value of [interim] is required to fire [loop 2]. The [connection] rule can determine this value.
REM A value of [reaction] is required to fire [connection]. The [loop 1] rule can determine this value.
REM A value of [action] is required to fire [loop 1]. The [loop 2] rule can determine this value -- and loop begins.

RULE [loop 1]
If [action] = true
Then [reaction] = false

RULE [connection]
If [reaction] = false
Then [interim] = true

RULE [loop 2]
If [interim] = true
Then [action] = true

PROMPT [interim] YesNo
"Is interim true?"

GOAL [action]