<PROPOSITION> ::=
<QN><TERM><COPULA><TERM>
<QN><TERM><COPULA><QL><TERM>
<SIGN><QN><TERM><COPULA><TERM>
<SIGN><QN><TERM><COPULA><QL><TERM>
<SIGNQN><TERM><COPULA><TERM>
<SIGNQN><TERM><COPULA><QL><TERM>
<SIGN> ::= not
<QN> ::= every | some
<TERM> ::= <VAR> | <CONST> | <CONJ>
<COPULA> ::= is | is not | is a | is not a
<QL> ::= un | non
<CONJ> ::= both <TERM> and <TERM> (and <TERM>)*
<TERM>
must also allow for expressing relations, e.g.:
<QN><TERM><COPULA><TERM><PREPOSITION><QN><TERM>
where <PREPOSITION>
is something like "of", "to", "from".