N. Goodman and W. V. Quine, "Steps Toward a Constructive Nominalism", Journal of Symbolic Logic, 12 (1947).

Symbol Convention

-->	=	material implication	<-->	=	material equivalence
&	=	conjunction	~	=	negation
V	=	disjunction	(x)	=	universal quantifier
(]x)	=	existential quantifier	^	=	concatenation
|	=	alternative denial (stroke)	epsilon	=	epsilon
=/=	=	not identical	.    :	=	parantheses