This is the fridge domain from UCPOP.  The only change is added a term 
"unscrewed" to handle the need for "not screwed" as a precondition,
"fridge-off" to handle "not fridge-on", "detached" for "not attached" and 
"not-in-place" for "not in-place".
Remember also that our parser is CASE-SENSITIVE....

(operator 
 unscrew
 (params (screw <x>) (backplane <y>))
 (preconds (screwed <x>) (holds <x> <y>))
 (effects (unscrewed <x>) (del screwed <x>)))

(operator 
 screw
 (params (screw <x>) (backplane <y>))
 (preconds (unscrewed <x>) (holds <x> <y>))
 (effects (del unscrewed <x>) (screwed <x>)))

(operator 
 remove-backplane
 (params (backplane <x>) (<f>) (<a>) (<b>) (<c>) (<d>))
 (preconds (in-place <x>) (part-of <x> <f>) (fridge-off <f>)
			  (holds <a> <x>)  (holds <b> <x>)  
			  (holds <c> <x>)  (holds <d> <x>)
			  (unscrewed <a>) (unscrewed <b>) 
			  (unscrewed <c>) (unscrewed <d>))
 (effects (not-in-place <x>) (del in-place <x>)))

(operator 
 attach-backplane
 (params (backplane <x>) (<f>) (<a>) (<b>) (<c>) (<d>))
 (preconds  (not-in-place <x>) (part-of <x> <f>) (fridge-off <f>)
	    (holds <a> <x>)  (holds <b> <x>) 
	    (holds <c> <x>)  (holds <d> <x>)
	    (unscrewed <a>) (unscrewed <b>)
	    (unscrewed <c>) (unscrewed <d>))
 (effects (del not-in-place <x>) (in-place <x>)))

(operator 
 start-fridge
 (params (<f>) (<a>) (<b>) (<c>) (<d>) (backplane <x>))
 (preconds  (in-place <x>) (part-of <x> <f>)
	    (holds <a> <x>)(holds <b> <x>)(holds <c> <x>)(holds <d> <x>)
	    (screwed <a>) (screwed <b>) (screwed <c>) (screwed <d>)
			  (fridge-off <f>))
 (effects (del fridge-off <f>) (fridge-on <f>)))

(operator 
 stop-fridge
 (params (<f>))
 (preconds (fridge-on <f>))
 (effects (fridge-off <f>) (del fridge-on <f>)))

(operator 
 change-compressor
 (params  (compressor <x>) (compressor <y>) (backplane <a>))
 (preconds (not-in-place <a>)
	   (covers <a> <x>) 
	   (attached <x>) (detached <y>))
 (effects (detached <x>) (del attached <x>) (attached <y>) (del detached <y>)
		    (del covers <a> <x>) (covers <a> <y>)))