Non-Empty Strings

The empty string "" is not equal to "grape". And "grape" is not equal to "". The empty string is not equal to any non-empty string.

A compact way of writing this rules is to use a symbol X to stand for the string of characters under consideration. Then:

equals( "", X )    = false if X is not the empty string

equals( X, "" )    = false if X is not the empty string

For example, equals( "", "hound") is false. In this example, X stands for "hound".

Also, equals( "poet", "") is false. This time, X stands for "poet".