code>boolean</code>, <code>number</code>, <code>string</code>, <code>function</code>, <code>thread</code> and <code>userdata</code>) may store in the object instance a mapping of each machted pairs so that <code>self[value] == other and self[other] == value</code> in order to avoid further evaluation of the same pair and that they are matched to other values.
	However, for positive integer numbers this should be avoided because these values are used to store the sequence of values that identifies the curren