def self.operators
@operators ||= ["and", "or", "is equal", "equals", "(is )?equal to", "is not",
"isn't", "isn't equal( to)?", "is not equal( to)?",
"doesn't equal", "does not equal", "(is )?greater than",
"comes after", "is not less than or equal( to)?",
"isn't less than or equal( to)?", "(is )?less than",
"comes before", "is not greater than or equal( to)?",
"isn't greater than or equal( to)?",
"(is )?greater than or equal( to)?", "is not less than",
"isn't less than", "does not come before",
"doesn't come before", "(is )?less than or equal( to)?",
"is not greater than", "isn't greater than",
"does not come after", "doesn't come after", "starts? with",
"begins? with", "ends? with", "contains?", "does not contain",
"doesn't contain", "is in", "is contained by", "is not in",
"is not contained by", "isn't contained by", "div", "mod",
"not", "(a )?(ref( to)?|reference to)", "is", "does"]
end