# Implication with `e` (implies).
	#
	# Note: it is transformed with conjunctions and disjunctions.
	#
	# ~~~
	# var a = new LVar("a")
	# var b = new LVar("b")
	# assert a.imp(b).to_s == "(~a | b)"
	# ~~~
	fun imp(e: LExpr): LExpr
	do
		return (~self) | e
	end