Let X < Y denote set X included in set Y.

This is called a subset and there is already a character used for it so you don't actually need to overload the < character. Even better, it is a named entity in HTML so even unicode-unfriendly sites can use it. The entity is called "sub" and here it is in use:

X ⊂ Y

If you use this to mean "X is a subset of Y" then the meaning should be clear to anyone familiar with set theory. HTH.

In reply to Re^2: Fast Way to find one array in second array by hippo
in thread Fast Way to find one array in second array by melmoth

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